Fix define_callbacks call

This was causing callbacks to be both before and after callbacks when set.

With the previous version, whilst spying on a method call, it was being called twice -- before and after, instead of only after. This patch fixes that, and the tests in this Rails 3.0.12 app now pass. 

That said, I must admit I was unable to get the tests working in this branch of AAA, after several tries. I know: I'm terrible.