Use auth cookie to stay logged in in Symfony if the session has expired.

Hi from Spain ;-)

Added a hook to authenticate user in Symfony if PHP session has expired. In this case WordPress parses the auth cookie and executes the auth_cookie_valid action. We hook into this mechanism.

The only downside I see is that now a query to get the logged in user is made for every wordpress page. But that's a "problem" that exists for pure Symfony applications as well.