Updating PHP version requirement for 13.1

PHP 5.3.10 offers several enhancements to the PHP stack, not the least of which is an arbitrary code execution bug that was fixed in that version.

Improvements to DirectoryIterator as well as a bugfix to BCRYPT (which allows us to properly implement password lib changes that are coming in PHP 5.5 right now) should also influence the decision.

More info on the change set can be found here. http://php.net/ChangeLog-5.php#5.3.10

Look at all the security fixes since 5.3.1 alone!