HDFS-5613. NameNode: implement handling of ACLs in combination with symlinks. Contributed by Chris Nauroth.

git-svn-id: https://svn.apache.org/repos/asf/hadoop/common/branches/HDFS-4685@1559804 13f79535-47bb-0310-9956-ffa450edef68
Merge branch 'HDFS-4685' into HADOOP-10241