Update versions & add PHP 5.6.

New versions :
* PHP 5.3.28
* PHP 5.4.24
* PHP 5.5.8
* PHP 5.6.0alpha1
Add gmp & pecl_http extensions to all versions.
Add specific files for PHP 5.6.x.

Compile the new phpdbg SAPI bundled with PHP 5.6.0alpha1.