- Fixed Query being able to join() from individual columns of

- Fixed Query being able to join() from individual columns of
a joined-table subclass entity, i.e.
query(SubClass.foo, SubcClass.bar).join(<anything>).
In most cases, an error "Could not find a FROM clause to join
from" would be raised. In a few others, the result would be
returned in terms of the base class rather than the subclass -
so applications which relied on this erroneous result need to be
adjusted. [ticket:1431]