HDFS-4434. Merge r1469644 from trunk.

git-svn-id: https://svn.apache.org/repos/asf/hadoop/common/branches/branch-2@1478282 13f79535-47bb-0310-9956-ffa450edef68
HDFS-4785. Merge change r1478267 from trunk

git-svn-id: https://svn.apache.org/repos/asf/hadoop/common/branches/branch-2@1478286 13f79535-47bb-0310-9956-ffa450edef68
HDFS-4784. Merge r1478276 from trunk

git-svn-id: https://svn.apache.org/repos/asf/hadoop/common/branches/branch-2@1478287 13f79535-47bb-0310-9956-ffa450edef68
Merge remote branch 'origin/branch-2' into branch-2-gd
Merge remote branch 'origin/branch-2-gd' into fb-MAPREDUCE-4884-branch-2-gd