- Fixed 1.0 regression where the "parent entity" of a synonym-

- Fixed 1.0 regression where the "parent entity" of a synonym-
mapped attribute on top of an :func:`.aliased` object would
resolve to the original mapper, not the :func:`.aliased`
version of it, thereby causing problems for a :class:`.Query`
that relies on this attribute (e.g. it's the only representative
attribute given in the constructor) to figure out the correct FROM
clause for the query.
fixes #3466
- apply consitency to ._parententity vs.
__clause_element__()._annotations['parententity']
in terms of aliased class, test it all.