Ability to mock classes with final constructors

1. Added check for isFinal when deciding on which strategy to use to obtain class instance.
2. Caught ReflectionException that happens when class is internal (see http://www.php.net/manual/en/reflectionclass.newinstancewithoutconstructor.php)
3. Added @ to surpress warnings some classes generate when being unserialised with empty properties (e.g. SimpleXmlElement complains node does not exist)