Basic support for rails 4.1

This is a few fixes to get forceps to mostly work with rails 4.1. I don't think its backwards compatible though.

I wasn't able to get has_and_belongs_to_many associations to work because they have completely changed in 4.1. They are now modeled as a has_many to a generated class. I'm excluding that generated class, so if you don't use that relationship, then forceps will work.
This is the main bit of work to get rails 4.1 to work, I don't think this is backwards compatible though.