HDFS-6480. Merge r1603705 from trunk.

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HDFS-6563. NameNode cannot save fsimage in certain circumstances when snapshots are in use. Contributed by Aaron T. Myers.


git-svn-id: https://svn.apache.org/repos/asf/hadoop/common/branches/branch-2@1603713 13f79535-47bb-0310-9956-ffa450edef68