Move YARN-84 to section 2.1.0-beta in CHANGES.txt.


git-svn-id: https://svn.apache.org/repos/asf/hadoop/common/trunk@1507587 13f79535-47bb-0310-9956-ffa450edef68
Move HDFS-3880 to section 2.1.0-beta in CHANGES.txt.


git-svn-id: https://svn.apache.org/repos/asf/hadoop/common/trunk@1507588 13f79535-47bb-0310-9956-ffa450edef68