- Fixed bug in Query involving order_by() in conjunction with

- Fixed bug in Query involving order_by() in conjunction with
multiple aliases of the same class (will add tests in
[ticket:1218])
- Added a new extension sqlalchemy.ext.serializer.  Provides
Serializer/Deserializer "classes" which mirror Pickle/Unpickle,
as well as dumps() and loads().  This serializer implements
an "external object" pickler which keeps key context-sensitive
objects, including engines, sessions, metadata, Tables/Columns,
and mappers, outside of the pickle stream, and can later
restore the pickle using any engine/metadata/session provider.
This is used not for pickling regular object instances, which are
pickleable without any special logic, but for pickling expression
objects and full Query objects, such that all mapper/engine/session
dependencies can be restored at unpickle time.