added support for multiple directories in $PHP_VERSIONS

Sometimes you have your different PHP versions installed in different directories.
For example, if you install PHP 5.3.21 and PHP 5.4.11 with homebrew (and you don't want to mess your FS with symlinks), you will have the below structure:

- /usr/local/Cellar/php53/5.3.21
- /usr/local/Cellar/php54/5.4.11

You can even image, want to have 5.3.21 and 5.4.10 installed with homebrew, and compile your own PHP version with debug symbols.
Looking for the right PHP version in multiple directories allow you that without having to simlink everything in the right directory.