Fix mocks to support >=5.5.14 and >=5.4.30

PHP 5.5.14 and PHP 5.4.30 disallow unseriliazing hand made strings for internal classes that forbids that (using zend_class_unserialize_deny)

There was a bug before, PHP did not filter those strings, which could lead to security problems.
Starting from 5.5.14 and 5.4.30 , PHP now reports an error when trying to unserialize such strings.
https://github.com/php/php-src/commit/2c88ae5c4ea8b641c407549d40c6ea61e834840d
PHPUnit relies on this (wrong) behavior to create mock objects. This is a problem for SPlFileInfo.

This PR fixes that.