HADOOP-10322. Add ability to read principal names from a keytab. Contributed by Benoy Antony and Daryn Sharp.

git-svn-id: https://svn.apache.org/repos/asf/hadoop/common/trunk@1590637 13f79535-47bb-0310-9956-ffa450edef68
HDFS-6218. Audit log should use true client IP for proxied webhdfs operations. Contributed by Daryn Sharp.

git-svn-id: https://svn.apache.org/repos/asf/hadoop/common/trunk@1590640 13f79535-47bb-0310-9956-ffa450edef68