HDFS-5100. Merging change r1514573 from trunk to branch-2.

git-svn-id: https://svn.apache.org/repos/asf/hadoop/common/branches/branch-2@1514574 13f79535-47bb-0310-9956-ffa450edef68
HDFS-5103. Merging change r1514576 from trunk to branch-2.

git-svn-id: https://svn.apache.org/repos/asf/hadoop/common/branches/branch-2@1514577 13f79535-47bb-0310-9956-ffa450edef68
MAPREDUCE-5462. In map-side sort, swap entire meta entries instead of indexes for better cache performance. (Sandy Ryza)

git-svn-id: https://svn.apache.org/repos/asf/hadoop/common/branches/branch-2@1514610 13f79535-47bb-0310-9956-ffa450edef68