Add transfer backend for UbuntuOne

[Jason Gerard DeRose]

So dmedia has a very abstract concept of a "store". A store can be the native dmedia FileStore somewhere on the local file system, or it can be a remote service like S3 or whatever.

Currently S3 (via boto) is the only proper remote store supported (both upload and download). You can see the S3 backend plugin here:

http://bazaar.launchpad.net/~dmedia/dmedia/trunk/view/head:/dmedia/backends/s3.py#L97

The base class may not be generic enough yet, may not have the right abstractions:

http://bazaar.launchpad.net/~dmedia/dmedia/trunk/view/head:/dmedia/transfers.py#L243

So this bug may take some slight changes to the TransferBackend base class.

Also, the UbuntuOne Files API doesn't yet support incremental upload (resumable upload), nor doesn't it support Range requests on the download side (needed for resumable download).

[Jason Gerard DeRose (jderose)]

As the future of Ubuntu One (at least the file sync part of it) seems a bit uncertain, I'm going to mark this as "wont fix". We can re-evaluate this in the future, of course.

For the time being, I think it's more important to focus on the native Dmedia file sync.