* docs for event listen kwargs
* docs for mysql to use `listen` for changing the sql_mode`

Change-Id: I7c1678488658edda3c5baaf0f7648108e93a4be1

Added some guards against ``KeyError`` in the event system to accommodate
the case that the interpreter is shutting down at the same time
:meth:`_engine.Engine.dispose` is being called, which would cause stack
trace warnings.

Fixes: #6740
Change-Id: I2c42e9edac2371e68b39d8360494c5fddfd6cd8c

Also replace http://pypi.python.org/pypi with https://pypi.org/project

Change-Id: I84b5005c39969a82140706472989f2a30b0c7685

Fixed critical regression caused by the change in :ticket`5497` where the
connection pool "init" phase no longer occurred within mutexed isolation,
allowing other threads to proceed with the dialect uninitialized, which
could then impact the compilation of SQL statements.

This issue is essentially the same regression which was fixed many years
ago in :ticket:`2964` in dd32540dabbee0678530fb1b0868d1eb41572dca,
which was missed this time as the test suite fo
that issue only tested the pool in isolation, and assumed the
"first_connect" event would be used by the Engine.  However
:ticket:`5497` stopped using "first_connect" and no test detected
the lack of mutexing, that has been resolved here through
the addition of more tests.

This fix also identifies what is probably a bug in earlier versions
of SQLAlchemy where the "first_connect" handler would be cancelled
if the initializer failed; this is evidenced by
test_explode_in_initializer which was doing a reconnect due to
c.rollback() yet wasn't hanging.  We now solve this issue by
preventing the manufactured Connection from ever reconnecting
inside the first_connect handler.

Also remove the "_sqla_unwrap" test attribute; this is almost
not used anymore however we can use a more targeted
wrapper supplied by the testing.engines.proxying_engine
function.

See if we can also open up Oracle for "ad hoc engines" tests
now that we have better connection management logic.

Fixes: #6337
Change-Id: I4a3476625c4606f1a304dbc940d500325e8adc1a

Uses the flake8 option per-file-ignores that was introduced in a recent
version of flake8 (3.7.+) to avoid having lots of "noqa" in import
only files

Change-Id: Ib4871d63bad7e578165615df139cbf6093479201

Repaired / implemented support for primary key constraint naming
conventions that use column names/keys/etc as part of the convention. In
particular, this includes that the :class:`.PrimaryKeyConstraint` object
that's automatically associated with a :class:`.schema.Table` will update
its name as new primary key :class:`_schema.Column` objects are added to
the table and then to the constraint. Internal failure modes related to
this constraint construction process including no columns present, no name
present or blank name present are now accommodated.

Fixes: #5919
Change-Id: Ic2800b50f4a4cd5978bec48cefea0a2e198e0123

Change-Id: Ic5bb19ca8be3cb47c95a0d3315d84cb484bac47c

* Fix subclass traversals to not run classes multiple times

* switch compiler visitor to use an attrgetter, to avoid
  an eval() at startup time

* don't pre-generate traversal functions, there's lots of these
  which are expensive to generate at once and most applications
  won't use them all; have it generate them on first use instead

* Some ideas about removing asyncio imports, they don't seem to
  be too signficant, apply some more simplicity to the overall
  "greenlet fallback" situation

Fixes: #5681
Change-Id: Ib564ddaddb374787ce3e11ff48026e99ed570933

Reworked the "setinputsizes()" set of dialect hooks to be correctly
extensible for any arbirary DBAPI, by allowing dialects individual hooks
that may invoke cursor.setinputsizes() in the appropriate style for that
DBAPI.   In particular this is intended to support pyodbc's style of usage
which is fundamentally different from that of cx_Oracle.  Added support
for pyodbc.

Fixes: #5649
Change-Id: I9f1794f8368bf3663a286932cfe3992dae244a10

Reworked the proxy creation used by scoped_session() to be
based on fully copied code with augmented docstrings and
moved it into langhelpers.  asyncio session, engine,
connection can now take
advantage of it so that all non-async methods are availble.

Overall implementation of most important accessors / methods
on AsyncConnection, etc. , including awaitable versions
of invalidate, execution_options, etc.

In order to support an event dispatcher on the async
classes while still allowing them to hold __slots__,
make some adjustments to the event system to allow
that to be present, at least rudimentally.

Fixes: #5628
Change-Id: I5eb6929fc1e4fdac99e4b767dcfd49672d56e2b2