HADOOP-8957. Merge r1420965 from trunk

git-svn-id: https://svn.apache.org/repos/asf/hadoop/common/branches/branch-2@1490115 13f79535-47bb-0310-9956-ffa450edef68
HDFS-4876. Fix the javadoc of FileWithSnapshot and move FileDiffList to FileWithSnapshot.


git-svn-id: https://svn.apache.org/repos/asf/hadoop/common/branches/branch-2@1490117 13f79535-47bb-0310-9956-ffa450edef68
HADOOP-9131. Merge r1420366 from trunk.

git-svn-id: https://svn.apache.org/repos/asf/hadoop/common/branches/branch-2@1490118 13f79535-47bb-0310-9956-ffa450edef68
HADOOP-9526. Merge 1490120 from trunk

git-svn-id: https://svn.apache.org/repos/asf/hadoop/common/branches/branch-2@1490121 13f79535-47bb-0310-9956-ffa450edef68
HADOOP-8982. Merge 1490124 from trunk

git-svn-id: https://svn.apache.org/repos/asf/hadoop/common/branches/branch-2@1490125 13f79535-47bb-0310-9956-ffa450edef68