fixed missing method error if denomalization newer called, cleaned up tests for mongoid 3

At some point it is necessary to include an extensions without using their functionality. I.e if you bundle your includes in an application model. In this case repair_denormalized! fails because the array denormalize_definitions is never set. To solve that denormalize_from and denormalize_to should test wether  denormalize_definitions is set.

The whole project seems to run fine on mongoid 3 but tests failed. I thought it is the best to raise all tests to mongoid 3.