svn merge -c 1488630 from trunk for moving HDFS-4826 to 2.1.0-beta.


git-svn-id: https://svn.apache.org/repos/asf/hadoop/common/branches/branch-2@1488631 13f79535-47bb-0310-9956-ffa450edef68
Merge remote branch 'origin/branch-2' into branch-2-gd
Merge remote branch 'origin/branch-2-gd' into fb-YAHOO-217-branch-2-gd