Fixed Inheritiance bug and Circular Reference Exception

* When using multiple `extends` in PHP, the order was wrong
* The circular reference path was incorrect when mixing PHP's `extend` and mapping extends, made the exception message less verbose.

Fixes https://github.com/symfony-cmf/RoutingAutoBundle/issues/90
I've done it to match the class name, to be sure the correct name is shown. It's already clear it's a circular reference, because of the specific exception type.