Refactored, sketch index selectors
Implemented index selection
Addressed Ghislain's review comments
Refactored
Added constantc
Fixed wrapper
Use of constants in mongo-wrapper. Relaxed selection criterions to choose an index in more cases.
Added index test
Removed commented line
Added comment
Improved comment
Merge pull request #420 from 28msec/enforce-optimal-index

Enforce optimal index