HDFS-6552. add DN storage to a BlockInfo will not replace the different storage from same DN. (Contributed by Amir Langer)

git-svn-id: https://svn.apache.org/repos/asf/hadoop/common/trunk@1603602 13f79535-47bb-0310-9956-ffa450edef68
HDFS-6551. Rename with OVERWRITE option may throw NPE when the target file/directory is a reference INode. Contributed by Jing Zhao.

git-svn-id: https://svn.apache.org/repos/asf/hadoop/common/trunk@1603612 13f79535-47bb-0310-9956-ffa450edef68