Preparing for 2.0.4-alpha release.

git-svn-id: https://svn.apache.org/repos/asf/hadoop/common/branches/branch-2.0.4-alpha@1466317 13f79535-47bb-0310-9956-ffa450edef68
Release notes for 2.0.4-alpha.

git-svn-id: https://svn.apache.org/repos/asf/hadoop/common/branches/branch-2.0.4-alpha@1466318 13f79535-47bb-0310-9956-ffa450edef68