Preparing for hadoop-2.1.0-beta release.

git-svn-id: https://svn.apache.org/repos/asf/hadoop/common/trunk@1496791 13f79535-47bb-0310-9956-ffa450edef68
Release notes for hadoop-2.1.0-beta.

git-svn-id: https://svn.apache.org/repos/asf/hadoop/common/trunk@1496797 13f79535-47bb-0310-9956-ffa450edef68
Merge remote branch 'origin/trunk' into trunk-gd
Merge remote branch 'origin/trunk-gd' into fb-HDFS-4310-trunk-gd