- added **kw to ClauseElement.compare(), so that we can smarten up the "use_get"...

- added **kw to ClauseElement.compare(), so that we can smarten up the "use_get" operation
- many-to-one relation to a joined-table subclass now uses get()
  for a simple load (known as the "use_get" condition),
  i.e. Related->Sub(Base), without the need
  to redefine the primaryjoin condition in terms of the base
  table. [ticket:1186]
- specifying a foreign key with a declarative column,
  i.e. ForeignKey(MyRelatedClass.id) doesn't break the "use_get"
  condition from taking place [ticket:1492]