Merge branch 'feature/mongo_2.6.5_expressions' into feature/mongo_2.6.5_expressions_SetIntersection
EAGLESIX-2715 Reviewed test cases, filled out some missing ones, refectored common code.
Merge branch 'feature/mongo_2.6.5_expressions_SetIntersection' of https://github.com/RiveraGroup/mungedb-aggregate into feature/mongo_2.6.5_expressions_SetIntersection