loosen the restrictions on ReflectionClass::newInstanceWithoutConstructor()

allow instantiating any class except internal classes with a final __construct().
see http://www.serverphorums.com/read.php?7,959450,987654#msg-987654 (and the whole thread) for the full discussion, but basically with the removal of the unserialize O: trick which allowed the instantiation of internal classes with a custom serializer there is no way to do that from the userland, and that breaks a bunch of libs/apps out there.
the original restriction was in place, because there are internal classes with custom object storage, where the object initialization happens in the __construct instead of the create_object hook, but for non final constructors it is already a problem which can occur (a class which has it's own __construct method which doesn't call parent::__construct() extending an internal class), so it is ok to allow the same problems surfacing here also.