svn merge -c 1611737 FIXES: HDFS-6599. 2.4 addBlock is 10 to 20 times slower compared to 0.23 (daryn)


git-svn-id: https://svn.apache.org/repos/asf/hadoop/common/branches/branch-2.5@1611739 13f79535-47bb-0310-9956-ffa450edef68