Add prefix support

[CrackerJackMack]

Add the ability to prefix all uploads in a container. This would just add a string to be beginning of the filenames mimicking a directory structure. An empty object of "application/directory" should probably be created if the prefix is using a forward slash "/".

[CrackerJackMack]

Hrm, this is proving to be more difficult than I originally planned due to delta_force_one() using set intersections and differences. While this was a great speed improvement, it's created a problem in comparing prefixed files.

The problem lies in the assumption that the remote object names will match the local object names from os.walk(). This is true right until you add prefix support. Then all the local files are missing the prefix. I could add the prefix to each of the files but then you end up local file names that don't exist. I could add it then remove it each time I went to reference the file but I don't know if that's any more elegant than manually performing the intersections and differences myself.

Thoughts?

[CrackerJackMack]

Closed with Commit 9c3592d