svn merge -c 1512091 from trunk for HADOOP-9820. RPCv9 wire protocol is insufficient to support multiplexing. Contributed by Daryn Sharp.


git-svn-id: https://svn.apache.org/repos/asf/hadoop/common/branches/branch-2.1.0-beta@1512097 13f79535-47bb-0310-9956-ffa450edef68