HDFS-4551. When copying bytes in DatanodeWebHdfsMethods OPEN, use 4096 buffer size to improve performance.  Contributed by Mark Wagner


git-svn-id: https://svn.apache.org/repos/asf/hadoop/common/branches/branch-1@1453706 13f79535-47bb-0310-9956-ffa450edef68
Move HDFS-4252 to 1.2.0 in CHANGES.txt.


git-svn-id: https://svn.apache.org/repos/asf/hadoop/common/branches/branch-1@1453711 13f79535-47bb-0310-9956-ffa450edef68