EZP-23494: Sync eZ Publish 5.4/2014.09 with Symfony-standard 2.5

https://jira.ez.no/browse/EZP-23494

Changes stuff to be in sync with symfony-standard, for instance uses php's session save handler out of the box.

Changes taken mainly from this diff: https://github.com/symfony/symfony-standard/compare/2.3...v2.5.5