HIVE-4804 parallel order by fails for small datasets (Navis via egc)

Submitted by:	Navis
Reviewed by:	Edward Capriolo


git-svn-id: https://svn.apache.org/repos/asf/hive/trunk@1500071 13f79535-47bb-0310-9956-ffa450edef68
Merge remote branch 'origin/trunk' into trunk-gd
Merge remote branch 'origin/trunk-gd' into fb-HIVE-4791-trunk-gd