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 really don't like it when I get an exception message which burps "Foobar" without any context. I don't think its user friendly that the developer has to infer the type of the exception by looking at the exception type, and in any case, the same exception can be used in multiple places and each has its own story to tell. I prefer English :)