MAPREDUCE-5746. Job diagnostics can implicate wrong task for a failed job. (Jason Lowe via kasha)

git-svn-id: https://svn.apache.org/repos/asf/hadoop/common/branches/branch-2@1567669 13f79535-47bb-0310-9956-ffa450edef68
HDFS-5879. Merge 1567704 from trunk.

git-svn-id: https://svn.apache.org/repos/asf/hadoop/common/branches/branch-2@1567705 13f79535-47bb-0310-9956-ffa450edef68
HDFS-5810. Unify mmap cache and short-circuit file descriptor cache (cmccabe)

git-svn-id: https://svn.apache.org/repos/asf/hadoop/common/branches/branch-2@1567728 13f79535-47bb-0310-9956-ffa450edef68