HDFS-5950. The DFSClient and DataNode should use shared memory segments to communicate short-circuit information (cmccabe)

git-svn-id: https://svn.apache.org/repos/asf/hadoop/common/trunk@1573433 13f79535-47bb-0310-9956-ffa450edef68
add missing file for HDFS-5950

git-svn-id: https://svn.apache.org/repos/asf/hadoop/common/trunk@1573434 13f79535-47bb-0310-9956-ffa450edef68