Log Message:
Update from version 0.4.7p1 to 0.5.6.

This updates to a new stable branch of SQLAlchemy.
The list of changes are too extensive to include verbatim here, the change
log for the 0.5.6 release (and the rest of the 0.5 releases) is available at
  http://www.sqlalchemy.org/trac/browser/sqlalchemy/tags/rel_0_5_6/CHANGES

These changes were submitted as PR#42260 by Fredrik Pettai.