Mixins revision.
* Alternate more powerful implementation.
  No need to pre-specify allowed extension points.
  If two mixing provide the same method, or a single mixing and the main method, then a coordination method is always generated.
  Handles the special preExecution case.
  Can handle any case by overriding conventionally named methods "_createMixinMethod_<forMethodName>".
* Cleanup of the "legacy" addIns code.
* Passed the tests on the first write up! (doesn't mean it will actually work...)
* Placed some notes here and there, for things I think should be fixed.
Merge pull request #1 from dcleao/mixins

Mixins revision.