YARN-1859. Fixed WebAppProxyServlet to correctly handle applications absent on the ResourceManager. Contributed by Zhijie Shen.
svn merge --ignore-ancestry -c 1579866 ../../trunk/


git-svn-id: https://svn.apache.org/repos/asf/hadoop/common/branches/branch-2.4@1579868 13f79535-47bb-0310-9956-ffa450edef68