Merged from trunk to branch-2. MAPREDUCE-5898. distcp to support preserving HDFS extended attributes(XAttrs). Contributed by Yi Liu. 

git-svn-id: https://svn.apache.org/repos/asf/hadoop/common/branches/branch-2@1602116 13f79535-47bb-0310-9956-ffa450edef68
Merge from trunk to branch-2. MAPREDUCE-5920. Add Xattr option in DistCp docs. Contributed by Yi Liu.

git-svn-id: https://svn.apache.org/repos/asf/hadoop/common/branches/branch-2@1602119 13f79535-47bb-0310-9956-ffa450edef68
Merge from trunk to branch-2. HDFS-6464. Support multiple xattr.name parameters for WebHDFS getXAttrs. Contributed by Yi Liu

git-svn-id: https://svn.apache.org/repos/asf/hadoop/common/branches/branch-2@1602125 13f79535-47bb-0310-9956-ffa450edef68
Merged from trunk to branch-2. HDFS-6375. Listing extended attributes with the search permission. Contributed by Charles Lamb

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