This is kind of a mixed bag of all kinds to help get us
to 1.4 betas.    The documentation stuff is a work in
progress.    Lots of other relatively small changes to
APIs and things.    More commits will follow to continue
improving the documentation and transitioning to the
1.4/2.0 hybrid documentation.  In particular some refinements
to Session usage models so that it can match Engine's
scoping / transactional patterns, and a decision to
start moving away from "subtransactions" completely.

* add select().from_statement() to produce FromStatement in an
  ORM context

* begin referring to select() that has "plugins" for the few edge
  cases where select() will have ORM-only behaviors

* convert dynamic.AppenderQuery to its own object that can use
  select(), though at the moment it uses Query to support legacy
  join calling forms.

* custom query classes for AppenderQuery are replaced by
  do_orm_execute() hooks for custom actions, a separate gerrit
  will document this

* add Session.get() to replace query.get()

* Deprecate session.begin->subtransaction.  propose within the
  test suite a hypothetical recipe for apps that rely on this
  pattern

* introduce Session construction level context manager,
  sessionmaker context manager, rewrite the whole top of the
  session_transaction.rst documentation.   Establish context manager
  patterns for Session that are identical to engine

* ensure same begin_nested() / commit() behavior as engine

* devise all new "join into an external transaction" recipe,
  add test support for it, add rules into Session so it
  just works, write new docs.  need to ensure this doesn't
  break anything

* vastly reduce the verbosity of lots of session docs as
  I dont think people read this stuff and it's difficult
  to keep current in any case

* constructs like case(), with_only_columns() really need
  to move to *columns, add a coercion rule to just change
  these.

* docs need changes everywhere I look.  in_() is not in
  the Core tutorial?  how do people even know about it?
  Remove tons of cruft from Select docs, etc.

* build a system for common ORM options like populate_existing
  and autoflush to populate from execution options.

* others?

Change-Id: Ia4bea0f804250e54d90b3884cf8aab8b66b82ecf

Several weeks of using the future_select() construct
has led to the proposal there be just one select() construct
again which features the new join() method, and otherwise accepts
both the 1.x and 2.x argument styles.   This would make
migration simpler and reduce confusion.

However, confusion may be increased by the fact that select().join()
is different  Current thinking is we may be better off
with a few hard behavioral changes to old and relatively unknown APIs
rather than trying to play both sides within two extremely similar
but subtly different APIs.  At the moment, the .join() thing seems
to be the only behavioral change that occurs without the user
taking any explicit steps.   Session.execute() will still
behave the old way as we are adding a future flag.

This change also adds the "future" flag to Session() and
session.execute(), so that interpretation of the incoming statement,
as well as that the new style result is returned, does not
occur for existing applications unless they add the use
of this flag.

The change in general is moving the "removed in 2.0" system
further along where we want the test suite to fully pass
even if the SQLALCHEMY_WARN_20 flag is set.

Get many tests to pass when SQLALCHEMY_WARN_20 is set; this
should be ongoing after this patch merges.

Improve the RemovedIn20 warning; these are all deprecated
"since" 1.4, so ensure that's what the messages read.
Make sure the inforamtion link is on all warnings.
Add deprecation warnings for parameters present and
add warnings to all FromClause.select() types of methods.

Fixes: #5379
Fixes: #5284
Change-Id: I765a0b912b3dcd0e995426427d8bb7997cbffd51
References: #5159

Added support for "CREATE SEQUENCE" and full :class:`.Sequence` support for
Microsoft SQL Server.  This removes the deprecated feature of using
:class:`.Sequence` objects to manipulate IDENTITY characteristics which
should now be performed using ``mssql_identity_start`` and
``mssql_identity_increment`` as documented at :ref:`mssql_identity`. The
change includes a new parameter :paramref:`.Sequence.data_type` to
accommodate SQL Server's choice of datatype, which for that backend
includes INTEGER and BIGINT.   The default starting value for SQL Server's
version of :class:`.Sequence` has been set at 1; this default is now
emitted within the CREATE SEQUENCE DDL for all backends.

Fixes: #4235
Fixes: #4633
Change-Id: I6aa55c441e8146c2f002e2e201a7f645e667b916

- Remove deprecated method ``get_primary_keys` in the :class:`.Dialect` and
  :class:`.Inspector` classes.
- Remove deprecated event ``dbapi_error`` and the method ``ConnectionEvents.dbapi_error`.
- Remove support for deprecated engine URLs of the form ``postgres://``.
- Remove deprecated dialect ``mysql+gaerdbms``.
- Remove deprecated parameter ``quoting`` from :class:`.mysql.ENUM`
  and :class:`.mysql.SET` in the ``mysql`` dialect.
- Remove deprecated function ``comparable_property``. and function
  ``comparable_using`` in the declarative extension.
- Remove deprecated function ``compile_mappers``.
- Remove deprecated method ``collection.linker``.
- Remove deprecated method ``Session.prune`` and parameter ``Session.weak_identity_map``.
  This change also removes the class ``StrongInstanceDict``.
- Remove deprecated parameter ``mapper.order_by``.
- Remove deprecated parameter ``Session._enable_transaction_accounting`.
- Remove deprecated parameter ``Session.is_modified.passive``.
- Remove deprecated class ``Binary``. Please use :class:`.LargeBinary`.
- Remove deprecated methods ``Compiled.compile``, ``ClauseElement.__and__`` and
  ``ClauseElement.__or__`` and attribute ``Over.func``.
- Remove deprecated ``FromClause.count`` method.
- Remove deprecated parameter ``Table.useexisting``.
- Remove deprecated parameters ``text.bindparams`` and ``text.typemap``.

- Remove boolean support for the ``passive`` parameter in ``get_history``.
- Remove deprecated ``adapt_operator`` in ``UserDefinedType.Comparator``.

Fixes: #4643
Change-Id: Idcd390c77bf7b0e9957907716993bdaa3f1a1763

Removed autocommit and legacy "for update" / "lockmode" elements
from selectable.py / query.py.  lockmode was removed from
selectable in 693938dd6fb2f3ee3e031aed4c62355ac97f3ceb
however was not removed from the ORM.

Also removes the ignore_nonexistent_tables option on
join().

Change-Id: I0cfcf9e6a8d4ef6432c9e25ef75173b3b3f5fd87
Partially-fixes: #4643

Execution of literal sql string is deprecated in the
:meth:`.Connection.execute` and a warning is raised when used stating
that it will be coerced to :func:`.text` in a future release.
To execute a raw sql string the new connection method
:meth:`.Connection.exec_driver_sql` was added, that will retain the previous
behavior, passing the string to the DBAPI driver unchanged.
Usage of scalar or tuple positional parameters in :meth:`.Connection.execute`
is also deprecated.

Fixes: #4848
Fixes: #5178
Change-Id: I2830181054327996d594f7f0d59c157d477c3aa9

Fixed regression in 1.3.14 due to :ticket:`4849` where a sys.exc_info()
call failed to be invoked correctly when a flush error would occur. Test
coverage has been added for this exception case.

Fixes: #5196
Change-Id: Ib59a58a3a9d4c9c6f4b751201b794816a9f70225

The :class:`.Session` object no longer initates a
:class:`.SessionTransaction` object immediately upon construction or after
the previous transaction is closed; instead, "autobegin" logic now
initiates the new :class:`.SessionTransaction` on demand when it is next
needed.  Rationale includes to remove reference cycles from a
:class:`.Session` that has been closed out, as well as to remove the
overhead incurred by the creation of :class:`.SessionTransaction` objects
that are often discarded immediately. This change affects the behavior of
the :meth:`.SessionEvents.after_transaction_create` hook in that the event
will be emitted when the :class:`.Session` first requires a
:class:`.SessionTransaction` be present, rather than whenever the
:class:`.Session` were created or the previous :class:`.SessionTransaction`
were closed.   Interactions with the :class:`.Engine` and the database
itself remain unaffected.

Fixes: #5074
Change-Id: I00b656eb5ee03d87104257a214214617aacae16c

A warning is emitted for a condition in which the :class:`.Session` may
implicitly swap an object out of the identity map for another one with the
same primary key, detaching the old one, which can be an observed result of
load operations which occur within the :meth:`.SessionEvents.after_flush`
hook.  The warning is intended to notify the user that some special
condition has caused this to happen and that the previous object may not be
in the expected state.

Fixes: #4890
Change-Id: Ide11c6b9f21ca67ff5a96266c521d0c56fd6af8d

Revised the formatting for :class:`.StatementError` when stringified. Each
error detail is broken up over multiple newlines instead of spaced out on a
single line.  Additionally, the SQL representation now stringifies the SQL
statement rather than using ``repr()``, so that newlines are rendered as is.
Pull request courtesy Nate Clark.

Fixes: #4500

Closes: #4501
Pull-request: https://github.com/sqlalchemy/sqlalchemy/pull/4501
Pull-request-sha: 60cc0ee68dc96b8f483a60d37bcb26b6c6d53efe

Change-Id: I79d8418b7495e5691c9a56f41e79495c26a967ff