Fixing CHANGES.txt for YARN-758 as it is now merged into branch-2.1-beta.
svn merge --ignore-ancestry -c 1520659 ../../trunk/


git-svn-id: https://svn.apache.org/repos/asf/hadoop/common/branches/branch-2@1520660 13f79535-47bb-0310-9956-ffa450edef68