Rewrite the keys to be not ambiguous for $ and .

[swankjesse]

At the moment we jump through giant unfortunate hoops to make an unambiguous call when looking up a type name. I think we probably want something like java.util/Map.Entry or java/util/Map.Entry that we can map to the various names we need to load during codegen and reflection.

#501

[JakeWharton]

Might be a dupe of #444, except not reported as a bug in this case.