Get CPK running on active record 4.1
Fix up create, some changes for update.
Fix join association on Active Record 4.1.x

Update the overridden build_constraint method to match changes made in
Active Record 4.1.0.
Merge pull request #189 from simonsouth/bug/fix-join-association-on-ar-4.1.x

Fix join association on Active Record 4.1.x
merged ar_4.1.x with master + fixed dependency issue