HADOOP-11250. fix endmacro of set_find_shared_library_without_version in CMakeLists (Yi Liu via Colin P. McCabe)
HDFS-7230. Add rolling downgrade documentation. Contributed by Tsz Wo Nicholas Sze.
HADOOP-11221. IdentityHashStore assumes System.identityHashCode() is non-negative. Contributed by Jinghui Wang
HDFS-3342. SocketTimeoutException in BlockSender.sendChunks could have a better error message. Contributed by Yongjun Zhang.
Merge branch 'apache-trunk' into HDFS-6385