MAPREDUCE-4920. Use security token protobuf definition from hadoop common. Contributed by Suresh Srinivas.
svn merge --ignore-ancestry -c 1429751 ../../trunk/


git-svn-id: https://svn.apache.org/repos/asf/hadoop/common/branches/branch-2@1429752 13f79535-47bb-0310-9956-ffa450edef68