HDFS-6007. Update documentation about short-circuit local reads (iwasakims via cmccabe)

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HDFS-6068. Disallow snapshot names that are also invalid directory names.  Contributed by sathish


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Add TestSnapshotNameWithInvalidCharacters.java for HDFS-6068.


git-svn-id: https://svn.apache.org/repos/asf/hadoop/common/trunk@1579005 13f79535-47bb-0310-9956-ffa450edef68
YARN-1705. Reset cluster-metrics on transition to standby. (Rohith via kasha)

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