added MapReduce.getMapKeySort() and MapReduce.getReduceKeySort(). This allows MapReduce implementations to sort their results. This has a direct advantage for Gremlin OLAP where order(), orderBy(), shuffle(), etc. can be sorted prior to serialization on disk. TinkerGraph and Giraph have been updated accordingly with Giraph needing a bit more work when getReduceKeySort() is defined. OrderTest has been connected to ProcessComputeSuite and it works. Sweeeeeet. More docs. Fixed #272