HDFS-4542. Webhdfs doesn't support secure proxy users. Contributed by Daryn Sharp.

git-svn-id: https://svn.apache.org/repos/asf/hadoop/common/trunk@1452978 13f79535-47bb-0310-9956-ffa450edef68
HDFS-4540. Namenode http server should use the web authentication keytab for spnego principal. Contributed by Arpit Gupta.

git-svn-id: https://svn.apache.org/repos/asf/hadoop/common/trunk@1453025 13f79535-47bb-0310-9956-ffa450edef68
HDFS-4519. Support overriding jsvc binary and log file locations when launching secure datanode. Contributed by Chris Nauroth.

git-svn-id: https://svn.apache.org/repos/asf/hadoop/common/trunk@1453050 13f79535-47bb-0310-9956-ffa450edef68
Merge remote branch 'origin/trunk' into trunk-gd
Merge remote branch 'origin/trunk-gd' into fb-HDFS-4312-trunk-gd