calculate trainee type at instantiation; support subclassing with self-referencing BaseTrainer class; allow a backing invoker to be specified for a stub; move thenStub() to WhenObject because returning a stub doesn't make sense for any of the other fluent constructs; raw type warning; add special WhenClass construct to be properly documented in a future commit

git-svn-id: https://svn.apache.org/repos/asf/commons/proper/proxy/branches/version-2.0-work@1515495 13f79535-47bb-0310-9956-ffa450edef68