Test the region observer's generated java type, not the ruby.

This requires us to give up our fancier mocking (constant replacement), but for it we gain the ability to test that it really implements the interface we think it does.

These shenanigans only apply to compiled ruby types.  I expect the vast majority of the library will be "plain", more easily-testable ruby code.
Try switching to a RegionObserver.

This breaks, but I'm pushing to toss it over to my emacs macro man.