Adjust PHP provisioning to allow older versions

I have to work on a couple of dozen PHP-based projects and they tend to run over several versions.

One of the huge benefits of Vagrant is not having to worry about this when doing local development.

This request includes changes to allow you to run with:

* Latest and greatest (PHP 5.5 right now)
* Previous stable (PHP 5.4 right now)
* The distributed version (PHP 5.3 with 12.04)

It changes the main php.sh to just install and prior to that you can optionally include one of the more up-to-date repositories