HADOOP-10220: Add ACL indicator bit to FsPermission.  Bringing in change from HDFS-4685-WIP branch.
HADOOP-10220: add Javadoc.
HADOOP-10220: remove special case in RawLocalFileSystem to strip + indicator.
HADOOP-10220: add tests and fix a bug.
HDFS-4685-WIP: merge HADOOP-10220 to HDFS-4685-WIP.