Fixed critical regression where the :class:`_orm.Session` could fail to
"autobegin" a new transaction when a flush occurred without an existing
transaction in place, implicitly placing the :class:`_orm.Session` into
legacy autocommit mode which commit the transaction. The
:class:`_orm.Session` now has a check that will prevent this condition from
occurring, in addition to repairing the flush issue.

Additionally, scaled back part of the change made as part of :ticket:`5226`
which can run autoflush during an unexpire operation, to not actually
do this in the case of a :class:`_orm.Session` using legacy
:paramref:`_orm.Session.autocommit` mode, as this incurs a commit within
a refresh operation.

Fixes: #6233

Change-Id: Ia980e62a090e39e3e2a7fb77c95832ae784cc9a5

Fixed critical regression caused by the new feature added as part of
:ticket:`1763`, eager loaders are invoked on unexpire operations. The new
feature makes use of the "immediateload" eager loader strategy as a
substitute for a collection loading strategy, which unlike the other
"post-load" strategies was not accommodating for recursive invocations
between mutually-dependent relationships, leading to recursion overflow
errors.

Fixes: #6232
Change-Id: Ifb2286281f40d1a04c24741261d4438659b6e3dd

Fixed regression where the :func:`_orm.subqueryload` loader strategy would
fail to correctly accommodate sub-options, such as a :func:`_orm.defer`
option on a column, if the "path" of the subqueryload were more than one
level deep.

Fixes: #6221
Change-Id: I2addef0be6aaa022fa1b2f20060c4f0769c3bdfb

Fixed regression where the :func:`_orm.merge_frozen_result` function relied
upon by the dogpile.caching example was not included in tests and began
failing due to incorrect internal arguments.

Fixes: #6211
Change-Id: I0b53d0f569c817994ad4827a3ddb1626fd2d082f

Fixed regression where the ORM compilation scheme would assume the function
name of a hybrid property would be the same as the attribute name in such a
way that an ``AttributeError`` would be raised, when it would attempt to
determine the correct name for each element in a result tuple. A similar
issue exists in 1.3 but only impacts the names of tuple rows. The fix here
adds a check that the hybrid's function name is actually present in the
``__dict__`` of the class or its superclasses before assigning this name;
otherwise, the hybrid is considered to be "unnamed" and ORM result tuples
will use the naming scheme of the underlying expression.

Fixes: #6215
Change-Id: I584c0c05efec957f4dcaccf5df371399a57dffe9

Fixed critical regression where the :meth:`_orm.Query.yield_per` method in
the ORM would set up the internal :class:`_engine.Result` to yield chunks
at a time, however made use of the new :meth:`_engine.Result.unique` method
which uniques across the entire result. This would lead to lost rows since
the ORM is using ``id(obj)`` as the uniquing function, which leads to
repeated identifiers for new objects as already-seen objects are garbage
collected. 1.3's behavior here was to "unique" across each chunk, which
does not actually produce "uniqued" results when results are yielded in
chunks. As the :meth:`_orm.Query.yield_per` method is already explicitly
disallowed when joined eager loading is in place, which is the primary
rationale for the "uniquing" feature, the "uniquing" feature is now turned
off entirely when :meth:`_orm.Query.yield_per` is used.

This regression only applies to the legacy :class:`_orm.Query` object; when
using :term:`2.0 style` execution, "uniquing" is not automatically applied.
To prevent the issue from arising from explicit use of
:meth:`_engine.Result.unique`, an error is now raised if rows are fetched
from a "uniqued" ORM-level :class:`_engine.Result` if any
:ref:`yield per <orm_queryguide_yield_per>` API is also in use, as the
purpose of ``yield_per`` is to allow for arbitrarily large numbers of rows,
which cannot be uniqued in memory without growing the number of entries to
fit the complete result size.

Fixes: #6206
Change-Id: I3770d1f2e9be44d82c83ca992afb912dcc17af05