HDFS-5698. Use protobuf to serialize / deserialize FSImage. Contributed by Haohui Mai.

git-svn-id: https://svn.apache.org/repos/asf/hadoop/common/trunk@1566359 13f79535-47bb-0310-9956-ffa450edef68
HDFS-5837. dfs.namenode.replication.considerLoad should consider decommissioned nodes. Contributed by Tao Luo.

git-svn-id: https://svn.apache.org/repos/asf/hadoop/common/trunk@1566410 13f79535-47bb-0310-9956-ffa450edef68
HDFS-4370. Fix typo Blanacer in DataNode. Contributed by Chu Tong.

git-svn-id: https://svn.apache.org/repos/asf/hadoop/common/trunk@1566422 13f79535-47bb-0310-9956-ffa450edef68