To me, `verify_method_missing` doesn't really read well for what this method does.  Instead, what do you think about this?

* Make `ensure_implemented` public.
* Remove `verify_method_missing` (you won't need it or anything like it once you make `ensure_implemented` public).
* In the `method_missing` definitions for `InstanceVerifyingMock` and `ClassVerifyingMock`, make the first line `__mock_proxy.ensure_implemented(message) if null_object?` rather than `__mock_proxy.verify_method_missing(message)`.

I think that would communicate better.  Thoughts?