1. According to the WebHDFS API doc, the default value should be an empty string. Filed
HDFS-4598 for trunk.
2. Oops, forgot to change FilterFileSystem.
3. Trunk has two post(..) methods but branch-1 only has one so that the change is not required.
4. The corresponding doc change in trunk is in
HDFS-4456. This patch includes all three JIRAs, HDFS-3598, HDFS-4456 and HDFS-4598.