HDFS-4633. Change attribution in CHANGES.txt to version 2.2.1.

git-svn-id: https://svn.apache.org/repos/asf/hadoop/common/trunk@1537345 13f79535-47bb-0310-9956-ffa450edef68
Merge remote branch 'origin/trunk' into trunk-gd
Merge remote branch 'origin/trunk-gd' into fb-YAHOO-218-trunk-gd