Merge -c 1479589 from branch-1 to branch-1.2 to fix MAPREDUCE-5206. Ensure that a job doesn't get added to RetiredJobs multiple times in JobTracker. Contributed by Arun C. Murthy.

git-svn-id: https://svn.apache.org/repos/asf/hadoop/common/branches/branch-1.2@1479591 13f79535-47bb-0310-9956-ffa450edef68