Applied an explicit "cause" to most if not all internally raised exceptions
that are raised from within an internal exception catch, to avoid
misleading stacktraces that suggest an error within the handling of an
exception.  While it would be preferable to suppress the internally caught
exception in the way that the ``__suppress_context__`` attribute would,
there does not as yet seem to be a way to do this without suppressing an
enclosing user constructed context, so for now it exposes the internally
caught exception as the cause so that full information about the context
of the error is maintained.

Fixes: #4849
Change-Id: I55a86b29023675d9e5e49bc7edc5a2dc0bcd4751

Change-Id: I08440dc25e40ea1ccea1778f6ee9e28a00808235

in trying to apply 2020 copyright to files, the pre-commit
hooks complain about random file issues.

- remove old corrections.py utility, this had something to do
  with repairing refs in the sphinx docs

- run pre commit hooks on all files

- formatting adjustments to work around code formatting collisions
  (long import lines that zimports can't rewrite correctly)

Change-Id: I260744866f69e902eb93665c7c728ee94d3371a2

Includes:

PassiveDefault
SchemaItem.quote
Table.useexisting
Table.quote_schema
Table.append_ddl_listener
MetaData.append_ddl_listener
Metadata.reflect kw parameter (use reflect() method)
DDL.execute_at
DDL.on

Partially-fixes: #4643
Closes: #4893
Pull-request: https://github.com/sqlalchemy/sqlalchemy/pull/4893
Pull-request-sha: 860eb6a253fe4a95685b4f5f3349b19823a304f3

Change-Id: I0f5b8a873e7581365ff8dba48eab358d9e8e7b13

Fixes: #4850

<!-- Provide a general summary of your proposed changes in the Title field above -->

### Description
<!-- Describe your changes in detail -->

Removes usage of `util.callable`.

### Checklist
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This pull request is:

- [ ] A documentation / typographical error fix
	- Good to go, no issue or tests are needed
- [x] A short code fix
	- please include the issue number, and create an issue if none exists, which
	  must include a complete example of the issue.  one line code fixes without an
	  issue and demonstration will not be accepted.
	- Please include: `Fixes: #<issue number>` in the commit message
	- please include tests.   one line code fixes without tests will not be accepted.
- [ ] A new feature implementation
	- please include the issue number, and create an issue if none exists, which must
	  include a complete example of how the feature would look.
	- Please include: `Fixes: #<issue number>` in the commit message
	- please include tests.

**Have a nice day!**

Closes: #4851
Pull-request: https://github.com/sqlalchemy/sqlalchemy/pull/4851
Pull-request-sha: a0ccdff2cb74f5e944d8baccc269c382b591c8e2

Change-Id: I79918f44becbc5dbefdc7ff65128695c1cabed1d

The :meth:`.Index.create` and :meth:`.Index.drop` methods now have a
parameter :paramref:`.Index.create.checkfirst`, in the same way as that of
:class:`.Table` and :class:`.Sequence`, which when enabled will cause the
operation to detect if the index exists (or not) before performing a create
or drop operation.

Fixes: #527
Change-Id: Idf994bc016359d0ae86cc64ccb20378115cb66d6

A major refactoring of all the functions handle all detection of
Core argument types as well as perform coercions into a new class hierarchy
based on "roles", each of which identify a syntactical location within a
SQL statement.  In contrast to the ClauseElement hierarchy that identifies
"what" each object is syntactically, the SQLRole hierarchy identifies
the "where does it go" of each object syntactically.   From this we define
a consistent type checking and coercion system that establishes well
defined behviors.

This is a breakout of the patch that is reorganizing select()
constructs to no longer be in the FromClause hierarchy.

Also includes a rename of as_scalar() into scalar_subquery(); deprecates
automatic coercion to scalar_subquery().

Partially-fixes: #4617
Change-Id: I26f1e78898693c6b99ef7ea2f4e7dfd0e8e1a1bd

This affects mostly docstrings, except in orm/events.py::dispose_collection()
where one parameter gets renamed: given that the method is
empty, it seemed reasonable to me to fix that too.

Closes: #4440
Pull-request: https://github.com/sqlalchemy/sqlalchemy/pull/4440
Pull-request-sha: 779ed75acb6142e1f1daac467b5b14134529bb4b

Change-Id: Ic0553fe97853054b09c2453af76d96363de6eb0e

A large change throughout the library has ensured that all objects, parameters,
and behaviors which have been noted as deprecated or legacy now emit
``DeprecationWarning`` warnings when invoked.   As the Python 3 interpreter now
defaults to displaying deprecation warnings, as well as that modern test suites
based on tools like tox and pytest tend to display deprecation warnings,
this change should make it easier to note what API features are obsolete.

See the notes added to the changelog and migration notes for further
details.

Fixes: #4393
Change-Id: If0ea11a1fc24f9a8029352eeadfc49a7a54c0a1b

- fix a few "seealso"s
- ComparableProprerty's "superseded in 0.7" becomes deprecated in 0.7

Backport to currently maintained doc versions 1.2, 1.1

Change-Id: Ib1fcb2df8673dbe5c4ffc47f3896a60d1dfcb4b2