HBASE-6295  Possible performance improvement in client batch operations: presplit and send in background - addendum

git-svn-id: https://svn.apache.org/repos/asf/hbase/trunk@1497800 13f79535-47bb-0310-9956-ffa450edef68
Merge remote branch 'origin/trunk' into trunk-gd
Merge remote branch 'origin/trunk-gd' into fb-HBASE-8559-trunk-gd