to protect against unknown conditions when splicing inner joins
together within joined eager loads with ``innerjoin=True``; if
some of the joins use a "secondary" table, the assertion needs to
unwrap further joins in order to pass.
fixes #3412

:ticket:`3341` where in the unusual case of a constraint that refers
to a mixture of :class:`.Column` objects and string column names
at the same time, the auto-attach-on-column-attach logic will be
skipped; for the constraint to be auto-attached in this case,
all columns must be assembled on the target table up front.
Added a new section to the migration document regarding the
original feature as well as this change.
fixes #3411

off again so that test fixtures setup/teardown instrumentation as
expected
- clean up test_extendedattr.py and fix it to no longer leak
itself outside by ensuring _reinstall_default_lookups is always called,
part of #3408
- Fixed bug where when using extended attribute instrumentation system,
the correct exception would not be raised when :func:`.class_mapper`
were called with an invalid input that also happened to not
be weak referencable, such as an integer.
fixes #3408

to clean up automatically.  references #3407

as failing with the new 'entity' key value added to
:attr:`.Query.column_descriptions`, the logic to discover the "from"
clause is again reworked to accommodate columns from aliased classes,
as well as to report the correct value for the "aliased" flag in these
cases.
fixes #3409

using descriptors; ensure that mock.patch() honors descriptor setters

old / new style, direct access, and ad-hoc patching and
unpatching as possible

functionality.   Added a new "soft invalidate" feature to the
connection pool at the level of the checked out connection wrapper
as well as the :class:`._ConnectionRecord`.  This works similarly
to a modern pool invalidation in that connections aren't actively
closed, but are recycled only on next checkout; this is essentially
a per-connection version of that feature.  A new event
:class:`.PoolEvents.soft_invalidate` is added to complement it.
fixes #3379

- Added new flag
:attr:`.ExceptionContext.invalidate_pool_on_disconnect`.
Allows an error handler within :meth:`.ConnectionEvents.handle_error`
to maintain a "disconnect" condition, but to handle calling invalidate
on individual connections in a specific manner within the event.

- Added new event :class:`.DialectEvents.do_connect`, which allows
interception / replacement of when the :meth:`.Dialect.connect`
hook is called to create a DBAPI connection.  Also added
dialect plugin hooks :meth:`.Dialect.get_dialect_cls` and
:meth:`.Dialect.engine_created` which allow external plugins to
add events to existing dialects using entry points.
fixes #3355

of ``entity`` to the :attr:`.Query.column_descriptions` accessor
would fail if the target entity was produced from a core selectable
such as a :class:`.Table` or :class:`.CTE` object.
fixes #3403  references #3320