HDFS-5053. NameNode should invoke DataNode APIs to coordinate caching. (Andrew Wang)

git-svn-id: https://svn.apache.org/repos/asf/hadoop/common/branches/HDFS-4949@1523145 13f79535-47bb-0310-9956-ffa450edef68
HDFS-5201. NativeIO: consolidate getrlimit into NativeIO#getMemlockLimit. (Contributed by Colin Patrick McCabe)

git-svn-id: https://svn.apache.org/repos/asf/hadoop/common/branches/HDFS-4949@1523153 13f79535-47bb-0310-9956-ffa450edef68