HDFS-5364. Add OpenFileCtx cache. Contributed by Brandon Li

git-svn-id: https://svn.apache.org/repos/asf/hadoop/common/trunk@1539834 13f79535-47bb-0310-9956-ffa450edef68
HDFS-5326. add modifyDirective to cacheAdmin (cmccabe)

git-svn-id: https://svn.apache.org/repos/asf/hadoop/common/trunk@1539839 13f79535-47bb-0310-9956-ffa450edef68
HDFS-5394: Fix race conditions in DN caching and uncaching (cmccabe)

git-svn-id: https://svn.apache.org/repos/asf/hadoop/common/trunk@1539909 13f79535-47bb-0310-9956-ffa450edef68
HDFS-5476. Snapshot: clean the blocks/files/directories under a renamed file/directory while deletion. Contributed by Jing Zhao.

git-svn-id: https://svn.apache.org/repos/asf/hadoop/common/trunk@1540142 13f79535-47bb-0310-9956-ffa450edef68
HDFS-5371. Let client retry the same NN when dfs.client.test.drop.namenode.response.number is enabled. Contributed by Jing Zhao.

git-svn-id: https://svn.apache.org/repos/asf/hadoop/common/trunk@1540197 13f79535-47bb-0310-9956-ffa450edef68
Merge remote-tracking branch: upstream/trunk