Fixed table loading under SQLAlchemy 0.5.3.

Fixed table loading under SQLAlchemy 0.5.3.

Apparently the secret property on a singleton hidden in the guts of
SQLAlchemy has been made private recently, so what I wanted to do (get a
list of all ORM classes) is now impossible.  I gave up on trying to find
a real solution and just slapped together something using dir().