Add a dedicated cookbook for phpunit.
Install phpunit as a PHP Archive (PHAR).

Installation of phpunit via pear will soon be no more supported. Stick
with a pear installation for PHP 5.2 though to be able to install a
phpunit version compatible with 5.2.
Cleanup PHAR files management.
Add support for PHP 5.6.0beta1.
Update the changelog with PHP 5.6.0beta1.