DATAMONGO-1008 - DefaultIndexOperations no considers 2dsphere, too.

We now also check for 2dsphere when inspecting index keys and create an geo IndexField in that case.

Original pull request: #210.
DATAMONGO-1008 - Polishing.

Slightly changed the implementation of the 2dsphere check, Minor refactorings in the test case.

Original pull request: #210.