HDFS-5067 Support symlink operations in NFS gateway. Contributed by Brandon Li

git-svn-id: https://svn.apache.org/repos/asf/hadoop/common/trunk@1522774 13f79535-47bb-0310-9956-ffa450edef68
HDFS-5192. NameNode may fail to start when dfs.client.test.drop.namenode.response.number is set. Contributed by Jing Zhao.

git-svn-id: https://svn.apache.org/repos/asf/hadoop/common/trunk@1522775 13f79535-47bb-0310-9956-ffa450edef68
Merge remote-tracking branch: upstream/trunk