Preparing for CDH4.5.0.2 development
HDFS-6289. HA failover can fail if there are pending DN messages for DNs which no longer exist. Contributed by Aaron T. Myers.

git-svn-id: https://svn.apache.org/repos/asf/hadoop/common/branches/branch-2@1591414 13f79535-47bb-0310-9956-ffa450edef68
(cherry picked from commit fe566a692b218c2678726e66ee3c5aaa7699d836)
(cherry picked from commit c130dd3525e8525f2cda9fc7d4878d0e71ef6f74)
Preparing for CDH4.5.0.2 release