HDFS-5526. Datanode cannot roll back to previous layout version. Contributed by Kihwal Lee.

git-svn-id: https://svn.apache.org/repos/asf/hadoop/common/trunk@1545322 13f79535-47bb-0310-9956-ffa450edef68
HDFS-5533. Symlink delete/create should be treated as DELETE/CREATE in snapshot diff report. Contributed by Binglin Chang.

git-svn-id: https://svn.apache.org/repos/asf/hadoop/common/trunk@1545357 13f79535-47bb-0310-9956-ffa450edef68
HADOOP-10126. LightWeightGSet log message is confusing. Contributed by Vinay.

git-svn-id: https://svn.apache.org/repos/asf/hadoop/common/trunk@1545376 13f79535-47bb-0310-9956-ffa450edef68