Merge -c 1523652 from trunk to branch-2 to fix YARN-1170. YARN & MapReduce proto definitions fixed to specify protobuf package as hadoop.yarn and hadoop.mapreduce respectively. Contributed by Binglin Chang.

git-svn-id: https://svn.apache.org/repos/asf/hadoop/common/branches/branch-2@1523653 13f79535-47bb-0310-9956-ffa450edef68