Depend on SQLAlchemy 0.9.4 or greater

This prevents a nasty traceback and possible database corruption on systems
which have a sqlalchemy installed that is too old (e.g., fedora 20).

Change-Id: I2b60ddb1d50b5913c2cf8e5a848f26720163d47a
Closes-Bug: 123
Merge "Depend on SQLAlchemy 0.9.4 or greater"