[FIX] Re-introduce PHP 5.2 compatibility for backend pi

Remove the namespaced code again for the release, as this
won't be a problem for 6.x for now due to the class mappings.

Change-Id: I840f9ed688b05304a11de49ec6e0137653f46456
Releases: 2.3
Resolves: #44722
Reviewed-on: http://review.typo3.org/31750
Reviewed-by: Stefan Neufeind <typo3.neufeind@speedpartner.de>
Tested-by: Stefan Neufeind <typo3.neufeind@speedpartner.de>