HDFS-6717. Merging change r1614125 from trunk

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svn merge -c 1614215 from trunk for HDFS-6739. Add getDatanodeStorageReport to ClientProtocol.


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HADOOP-10876. The constructor of Path should not take an empty URL as a parameter. Contributed by Zhihai Xu.

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HADOOP-10821. Prepare the release notes for Hadoop 2.5.0. (Andrew Wang and Karthik Kambatla via kasha)

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HADOOP-8069: Merging r1614242 from trunk to branch-2.

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