HDFS-7201. Fix typos in hdfs-default.xml. Contributed by Dawson Choong.
YARN-2656. Made RM web services authentication filter support proxy user. Contributed by Varun Vasudev and Zhijie Shen.

(cherry picked from commit 1220bb72d452521c6f09cebe1dd77341054ee9dd)
HDFS-7190. Bad use of Preconditions in startFileInternal(). Contributed by Dawson Choong.
Merge remote-tracking branch 'remotes/origin/branch-2' into branch-2