better association messages

At first I was hoping to knock out association-related questions like thiese:

- http://stackoverflow.com/questions/24480659/self-joins-in-batmanjs/24481108#comment37934439_24481108
- http://stackoverflow.com/questions/21368596/batman-js-related-model-undefined-for-polymorphic-association-not-found-same-n

Then I threw in some `Batman.functionName`s just for consistency