HDFS-6665. Add tests for XAttrs in combination with viewfs. Contributed by Stephen Chu.

git-svn-id: https://svn.apache.org/repos/asf/hadoop/common/branches/branch-2@1614546 13f79535-47bb-0310-9956-ffa450edef68
HDFS-6778. The extended attributes javadoc should simply refer to the user docs. Contributed by Charles Lamb.

git-svn-id: https://svn.apache.org/repos/asf/hadoop/common/branches/branch-2@1614548 13f79535-47bb-0310-9956-ffa450edef68