HDFS-5291. Standby namenode after transition to active goes into safemode. Contributed by Jing Zhao.

git-svn-id: https://svn.apache.org/repos/asf/hadoop/common/trunk@1530112 13f79535-47bb-0310-9956-ffa450edef68
HDFS-5317. Go back to DFS Home link does not work on datanode webUI. Contributed by Haohui Mai

git-svn-id: https://svn.apache.org/repos/asf/hadoop/common/trunk@1530114 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