- an existing state shouldn't need its load_options/load_path updated;
it should maintain those from its original Query source.  there's no
tests that check this behavior

Found using: https://github.com/intgr/topy

- move out logging tests from test_execute to test_logging

version id programmatically outside of the generator.   using this system,
we can also leave the version id alone.

- modernize test for that
- use py3k compatible next() in test_returning/test_versioning

to rely upon server generated version identifiers, using triggers
or other database-provided versioning features, by passing the value
``False``.  The ORM will use RETURNING when available to immediately
load the new version identifier, else it will emit a second SELECT.
[ticket:2793]
- The ``eager_defaults`` flag of :class:`.Mapper` will now allow the
newly generated default values to be fetched using an inline
RETURNING clause, rather than a second SELECT statement, for backends
that support RETURNING.
- Added a new variant to :meth:`.ValuesBase.returning` called
:meth:`.ValuesBase.return_defaults`; this allows arbitrary columns
to be added to the RETURNING clause of the statement without interfering
with the compilers usual "implicit returning" feature, which is used to
efficiently fetch newly generated primary key values.  For supporting
backends, a dictionary of all fetched values is present at
:attr:`.ResultProxy.returned_defaults`.
- add a glossary entry for RETURNING
- add documentation for version id generation, [ticket:867]