Add again Propel from sfDatabaseSessionStorage

[mmonguilod]

I'm trying to use your fork to substitute symfony 1.4 in a project with Propel, but the changes mades in the commit 6aefb3c prevents us to use because we are saving the session data in a database to balance load between servers.

Please, can you revert this change? This does not affect to people that uses Doctrine, but allows the use of Propel with your fork. This way we have not to fork just to change on file of the core.

[GromNaN]

I agree that this change can be reverted. Can you make a PR ?

[j0k3r]

👍

[mmonguilod]

I've just made the PR. Thanks