Add a sed patch to fix an import bug.

From http://elixir.ematia.de/trac/ticket/121:

> SQLAlchemy 0.8 moved ScopedSession from sqlalchemy.orm.scoping, so the import from sqlalchemy.orm in entity.py does not work anymore.
>
>     from sqlalchemy.orm.scoping import ScopedSession
>
> works

Resolves #14 and #15