HDFS-5096. Automatically cache new data added to a cached path (contributed by Colin Patrick McCabe)

git-svn-id: https://svn.apache.org/repos/asf/hadoop/common/branches/HDFS-4949@1532924 13f79535-47bb-0310-9956-ffa450edef68
add missing file for HDFS-5096

git-svn-id: https://svn.apache.org/repos/asf/hadoop/common/branches/HDFS-4949@1532925 13f79535-47bb-0310-9956-ffa450edef68