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

git-svn-id: https://svn.apache.org/repos/asf/hadoop/common/branches/branch-0.23@1452981 13f79535-47bb-0310-9956-ffa450edef68
HDFS-4553. Webhdfs will NPE on some unexpected response codes. Contributed by Daryn Sharp.

git-svn-id: https://svn.apache.org/repos/asf/hadoop/common/branches/branch-0.23@1452994 13f79535-47bb-0310-9956-ffa450edef68
Merge remote branch 'origin/branch-0.23' into branch-0.23-gd