* Delegated logic from the double to the proxy, since it is near by and
already knows how to check if a method is implemented.
* No additional documentation, since this is the least surprising
* Not sufficient duplication to warrant DRYing up the verifying method_missing
implementations, if these classes start to look any more alike I would
consider it though.
* verify_method_missing is a terrible method name, but I wanted to tell
rather than ask rather than including the null object conditional in
the method_missing implementation.