consider "inspect(_of_type)" to be the entity of a comparator

consider "inspect(_of_type)" to be the entity of a comparator

Fixed 1.4 regression where :meth:`_orm.Query.filter_by` would not function
correctly when :meth:`_orm.Query.join` were joined to an entity which made
use of :meth:`_orm.PropComparator.of_type` to specify an aliased version of
the target entity. The issue also applies to future style ORM queries
constructed with :func:`_sql.select`.

Fixes: #7244
Change-Id: Ied28a03ce93201f932c7172d283cd4297be4d592