HDFS-4832. Namenode doesn't change the number of missing blocks in safemode when DNs rejoin or leave. Contributed by Ravi Prakash.

git-svn-id: https://svn.apache.org/repos/asf/hadoop/common/branches/branch-0.23@1490806 13f79535-47bb-0310-9956-ffa450edef68
Fix misplaced CHANGES.txt entry for HDFS-4867.

git-svn-id: https://svn.apache.org/repos/asf/hadoop/common/branches/branch-0.23@1490807 13f79535-47bb-0310-9956-ffa450edef68
Merge remote branch 'origin/branch-0.23' into branch-0.23-gd
Merge remote branch 'origin/branch-0.23-gd' into fb-YAHOO-225-branch-0.23-gd