Fixes #311 PHP fatal error

Due to a memory handling issue in PHP core Mocks might cause PHP to error out when called in a destructor.

The workaround works because it causes ReflectionClass to create a new class entry and not reuse the one from the existing object. Alternatively ``ReflectionClass`` could be replaced with ``ReflectionObject``.

Relevant part of the code: http://lxr.php.net/xref/PHP_5_5/ext/reflection/php_reflection.c#3313

Any chance to get this in a tagged release quickly? It kinda gets in the way of my SwiftMailer work ;)