MAPREDUCE-5053. java.lang.InternalError from decompression codec cause reducer to fail (Robert Parker via jeagles)

git-svn-id: https://svn.apache.org/repos/asf/hadoop/common/branches/branch-0.23@1458368 13f79535-47bb-0310-9956-ffa450edef68
MAPREDUCE-4990. Construct debug strings conditionally in ShuffleHandler.Shuffle#sendMapOutput(). (kkambatl via tgraves)

git-svn-id: https://svn.apache.org/repos/asf/hadoop/common/branches/branch-0.23@1458376 13f79535-47bb-0310-9956-ffa450edef68
MAPREDUCE-5028. Maps fail when io.sort.mb is set to high value. (kkambatl via tgraves)

git-svn-id: https://svn.apache.org/repos/asf/hadoop/common/branches/branch-0.23@1458380 13f79535-47bb-0310-9956-ffa450edef68
Merge remote branch 'origin/branch-0.23' into branch-0.23-gd
Merge remote branch 'origin/branch-0.23-gd' into fb-HADOOP-7435-branch-0.23-gd