HDFS-5514. FSNamesystem's fsLock should allow custom implementation (daryn)


git-svn-id: https://svn.apache.org/repos/asf/hadoop/common/trunk@1548161 13f79535-47bb-0310-9956-ffa450edef68
Neglected to add new file in HDFS-5514 (daryn)


git-svn-id: https://svn.apache.org/repos/asf/hadoop/common/trunk@1548167 13f79535-47bb-0310-9956-ffa450edef68