Provide Demeter-violating stubbing extension

Rails association proxies and named-scopes are sometimes cumbersome to mock because of the necessary (?) train-wreck code. Flexmock provides a mechanism to make setting up stubs for such code terser. We should consider adding something like this to Mocha, but I think it should be an optional extension.

See http://groups.google.com/group/m...

See also "Mocking Law of Demeter Violations" section of Flexmock docs http://flexmock.rubyforge.org/