YARN-1121. Addendum patch. Fixed AsyncDispatcher hang issue during stop due to a race condition caused by the previous patch. Contributed by Jian He.
svn merge --ignore-ancestry -c 1554344 ../../trunk/


git-svn-id: https://svn.apache.org/repos/asf/hadoop/common/branches/branch-2@1554345 13f79535-47bb-0310-9956-ffa450edef68