Fixed bug in new SQL comments feature where table and column comment
would not be copied when using :meth:`.Table.tometadata`.

Change-Id: Ib3112e5e02930245daacb36c8ed38c01fa3e7dbd
Fixes: #4087

Added a new method :class:`.DefaultExecutionContext.current_parameters`
which is used within a function-based default value generator in
order to retrieve the current parameters being passed to the statement.
The new function differs from the ``.current_parameters`` attribute in
that it also provides for optional grouping of parameters that
correspond to a multi-valued "insert" construct.  Previously it was not
possible to identify the subset of parameters that were relevant to
the function call.

Change-Id: I6894c7b4a2bce3e83c3ade8af0e5b2f8df37b785
Fixes: #4075

Fixes: #3429

Co-authored-by: Mike Bayer <mike_mp@zzzcomputing.com>
Change-Id: I870ee7dc801d553c5309c291402ec468b671e9a9
Pull-request: https://github.com/zzzeek/sqlalchemy/pull/383

Drops support for cx_Oracle prior to version 5.x, reworks
numeric and binary support.

Fixes: #4064

Change-Id: Ib9ae9aba430c15cd2a6eeb4e5e3fd8e97b5fe480

Refined the behavior of :meth:`.Operators.op` such that in all cases,
if the :paramref:`.Operators.op.is_comparison` flag is set to True,
the return type of the resulting expression will be
:class:`.Boolean`, and if the flag is False, the return type of the
resulting expression will be the same type as that of the left-hand
expression, which is the typical default behavior of other operators.
Also added a new parameter :paramref:`.Operators.op.return_type` as well
as a helper method :meth:`.Operators.bool_op`.

Change-Id: Ifc8553cd4037d741b84b70a9702cbd530f1a9de0
Fixes: #4063

SQL Server supports what SQLAlchemy calls "native boolean"
with its BIT type, as this type only accepts 0 or 1 and the
DBAPIs return its value as True/False.   So the SQL Server
dialects now enable "native boolean" support, in that a
CHECK constraint is not generated for a :class:`.Boolean`
datatype.  The only difference vs. other native boolean
is that there are no "true" / "false" constants so "1" and
"0" are still rendered here.

Tests are implicit in the existing suites.

Change-Id: I75bbcd549884099fb1a177e68667bf880c40fa7c
Fixes: #4061

Fixed bug in new percent-sign support (e.g. :ticket:`3740`) where a bound
parameter rendered with literal_binds would fail to escape percent-signs
for relevant dialects.  In addition, ensured new table / column comment
support feature also fully makes use of literal-rendered parameters so that
this percent sign support takes place with table / column comment DDL as
well, allowing percent sign support for the mysql / psycopg2 backends that
require escaping of percent signs.

Change-Id: Ia4136a300933e9bc6a01a7b9afd5c7b9a3fee4e3
Fixes: #4054
Fixes: #4052

Altered the range specification for window functions to allow
for two of the same PRECEDING or FOLLOWING keywords in a range
by allowing for the left side of the range to be positive
and for the right to be negative, e.g. (1, 3) is
"1 FOLLOWING AND 3 FOLLOWING".

Change-Id: I7d3a6c641151bb49219104968d18dac2266f3db8
Fixes: #4053

Fixed bug where an index reflected under Oracle with an expression like
"column DESC" would not be returned, if the table also had no primary
key, as a result of logic that attempts to filter out the
index implicitly added by Oracle onto the primary key columns.

Reworked the "filter out the primary key index" logic in oracle
get_indexes() to be clearer.

This changeset also adds an internal check to ColumnCollection
to accomodate for the case of a column being added twice,
as well as adding a private _table argument to Index such that
reflection can specify the Table explicitly.  The _table
argument can become part of public API in a later revision
or release if needed.

Change-Id: I745711e03b3e450b7f31185fc70e10d3823063fa
Fixes: #4042