Improve local tests on PHP-FPM.

Instead of running a loose version check on PHP-FPM, the assertion of
local tests now checks FPM configuration for errors.
Adds installation of PECL packages.

As many pecl packages also require another libraries to be installed an
option `php_packages_extra` was created to allow addition of another
packages to be installed in the operating system without affecting
installation of PHP packages (and their definitions).
Merge pull request #20 from augustohp/pecl_extensions

Pecl extensions installation