Update index page

git-svn-id: https://svn.apache.org/repos/asf/hama/trunk@1496699 13f79535-47bb-0310-9956-ffa450edef68
Update CHANGES.txt

git-svn-id: https://svn.apache.org/repos/asf/hama/trunk@1496700 13f79535-47bb-0310-9956-ffa450edef68
Merge branch 'trunk' of http://github.com/apache/hama into trunk
For performance, skip the resending message in aggregator.