Fix compatibility with Rails 4/Arel 4.0.1.

The method signature of the Arel stuff changed in the 4.0.1 release:
https://github.com/rails/arel/commit/68a95542e1a7a79d9777223fbffd2b982fed0268

This adds some basic tests surrounding this Arel functionality using a
FakeRecord class taken from how Arel performs its own tests.
Use Appraisal to make local testing with multiple Rails versions easier
See about cleaning up rubinius support on Travis.
Merge branch 'arel401'