When optional classes and php extensions like pgsql and additonal Zend-Pdos are
actually required by creating a new resource or authentication backend,
perform a check and display a warning instead of just throwing an exception.
refs #4788
Store messages in the current user session to be able to fetch messages from
other controllers, so that the use can be redirected back to the index, instead
of staying in the original action
refs #5100
Matthias Jentsch
Johannes Meyer