HDFS-4342. Directories configured in dfs.namenode.edits.dir.required but not in dfs.namenode.edits.dir are silently ignored.  Contributed by Arpit Agarwal


git-svn-id: https://svn.apache.org/repos/asf/hadoop/common/trunk@1445006 13f79535-47bb-0310-9956-ffa450edef68
merge trunk to HDFS-4249 with manual resolution for HDFS-4342
HDFS-4372: correct NullPointerException problems from prior merge