MAPREDUCE-4049. Experimental api to allow for alternate shuffle plugins. Contributed by Anver BenHanoch.

git-svn-id: https://svn.apache.org/repos/asf/hadoop/common/branches/branch-2@1438793 13f79535-47bb-0310-9956-ffa450edef68
MAPREDUCE-4809. Change visibility of classes for pluggable sort changes. (masokan via tucu)

git-svn-id: https://svn.apache.org/repos/asf/hadoop/common/branches/branch-2@1438794 13f79535-47bb-0310-9956-ffa450edef68
MAPREDUCE-4807. Allow MapOutputBuffer to be pluggable. (masokan via tucu)

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MAPREDUCE-4808. Refactor MapOutput and MergeManager to facilitate reuse by Shuffle implementations. (masokan via tucu)

git-svn-id: https://svn.apache.org/repos/asf/hadoop/common/branches/branch-2@1438796 13f79535-47bb-0310-9956-ffa450edef68
MAPREDUCE-2264. Job status exceeds 100% in some cases. (devaraj.k and sandyr via tucu)

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svn merge -c 1438808 from trunk for HDFS-4443. Remove a trailing '`' character from the HTML code generated by NamenodeJspHelper.generateNodeData(..).


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