HDFS-4772. Merging change r1495253 from trunk

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Merge r1495533 from trunk to branch-2 for YARN-827. Need to make Resource arithmetic methods accessible (Jian He via bikas)

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Update CHANGES.txt to move HDFS-4772 to 2.1.0 section

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Merged HADOOP-9619 svn merge -c 1495564


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svn merge -c 1495577 FIXES: HADOOP-9421. [RPC v9] Convert SASL to use ProtoBuf and provide negotiation capabilities (daryn)


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