[TASK] Raise PHP version requirement to 5.3.7

PHP versions smaller than 5.3.7 have some bugs that are worked
around with some nasty hacks in current core. It was already
decided on TYPO3 Active Contributor Meeting in Nuernberg to
not support these versions with the upcoming LTS that will have
to support so many different PHP versions already: Younger 5.3,
5.4, 5.5 and later on in the lifecycle of the product maybe even
more.

The patch drops compatibility code for versions smaller than 5.3.7.

Change-Id: I3344d797f0c2f23f5135257b98c1b05c80871399
Resolves: #50529
Releases: 6.2
Reviewed-on: https://review.typo3.org/22662
Reviewed-by: Wouter Wolters
Tested-by: Wouter Wolters
Reviewed-by: Stefan Neufeind
Tested-by: Stefan Neufeind