Change-Id: I08440dc25e40ea1ccea1778f6ee9e28a00808235

Fixed issue in event system where using the ``once=True`` flag with
dynamically generated listener functions would cause event registration of
future events to fail if those listener functions were garbage collected
after they were used, due to an assumption that a listened function is
strongly referenced.  The "once" wrapped is now modified to strongly
reference the inner function persistently, and documentation is updated
that using "once" does not imply automatic de-registration of listener
functions.

Fixes: #4794
Change-Id: I06388083d1633dcc89e8919eb1e51270f966df38

These changes should be ported from 1.3 back to 1.0 or
possibly 0.9 to the extent they are relevant in each
version. In 1.3 we hope to turn all deprecation documentation
into warnings.

Change-Id: I205186cde161af9389af513a425c62ce90dd54d8

Change-Id: I6a71f4924d046cf306961c58dffccf21e9c03911

Applied on top of a pure run of black -l 79 in
I7eda77fed3d8e73df84b3651fd6cfcfe858d4dc9,  this set of changes
resolves all remaining flake8 conditions for those codes
we have enabled in setup.cfg.

Included are resolutions for all remaining flake8 issues
including shadowed builtins, long lines, import order, unused
imports, duplicate imports, and docstring issues.

Change-Id: I4f72d3ba1380dd601610ff80b8fb06a2aff8b0fe

This is a straight reformat run using black as is, with no edits
applied at all.

The black run will format code consistently, however in
some cases that are prevalent in SQLAlchemy code it produces
too-long lines.   The too-long lines will be resolved in the
following commit that will resolve all remaining flake8 issues
including shadowed builtins, long lines, import order, unused
imports, duplicate imports, and docstring issues.

Change-Id: I7eda77fed3d8e73df84b3651fd6cfcfe858d4dc9

Change-Id: I3ef36bfd0cb0ba62b3123c8cf92370a43156cf8f

Change-Id: I4e8c2aa8fe817bb2af8707410fa0201f938781de