change a bit the mock engine to allow extension...

[Grummfy]

I think we should change a bit the behavior on the mock.
For now, if we want to change the behavior of it, we need to do what the visibility extension do, replace the mock generator with a child class. This doesn't allow atoum to be extended multiple time or you need to deal with conflict of multiple extension doing the same.

Example, the extension that I have (not publish for this reason) about trait, is become a bit harder because of this reason. So did you have any idea how we can improve a bit our mock engine to allow theses change and make it extendable?

Thanks