Preparing for hadoop-2.1.0-beta release.

git-svn-id: https://svn.apache.org/repos/asf/hadoop/common/branches/branch-2.1-beta@1496792 13f79535-47bb-0310-9956-ffa450edef68
Release notes for hadoop-2.1.0-beta.

git-svn-id: https://svn.apache.org/repos/asf/hadoop/common/branches/branch-2.1-beta@1496799 13f79535-47bb-0310-9956-ffa450edef68