HIVE-1402 Add parallel order by to hive (Navis Ryu and Jeff Zhang via egc)

Submitted by:	Navis Ryu
Reviewed by:	Edward Capriolo


git-svn-id: https://svn.apache.org/repos/asf/hive/trunk@1495847 13f79535-47bb-0310-9956-ffa450edef68
Merge remote-tracking branch 'upstream/trunk' into HIVE-4781
do not emit in the middle of a key group for left semi joins