HDFS-6039. Uploading a File under a Dir with default acls throws "Duplicated ACLFeature". Contributed by Chris Nauroth.

git-svn-id: https://svn.apache.org/repos/asf/hadoop/common/trunk@1573879 13f79535-47bb-0310-9956-ffa450edef68
HDFS-6040. fix DFSClient issue without libhadoop.so and some other ShortCircuitShm cleanups (cmccabe)

git-svn-id: https://svn.apache.org/repos/asf/hadoop/common/trunk@1573883 13f79535-47bb-0310-9956-ffa450edef68
HDFS-6046. add dfs.client.mmap.enabled (cmccabe)

git-svn-id: https://svn.apache.org/repos/asf/hadoop/common/trunk@1573887 13f79535-47bb-0310-9956-ffa450edef68