Fix compatibility with activerecord 4.1.2.rc1

where_values_hash now taskes the reflection name as an argument, so we
need to update the monkey patch. This should be fully backwards
compatible.
Merge pull request #354 from felixbuenemann/rails-4.1.2.rc1-compatibility

Fix compatibility with activerecord 4.1.2.rc1
Use reflections or _reflections, whichever is defined.

Not beautiful, but this should fix #353 for now. Also see
rails/rails#15300.