syncdaemon mixes uniqueness, cancels, and uploading/downloading dictionaries

[Lucio Torre]

When syncdaemon adds an upload, it will check in uploading to see if it should be removed. Then it will also remove it from the list in some other place, and somewhere else you also have to cancel the transfer. This should be simplified so that stuff like https://bugs.launchpad.net/ubuntuone-client/+bug/705231 does no happen again.

[Facundo Batista (facundo)]

This has three sides:

- Cancel the previous upload when Upload/Download detects other command because their uniqueness. Note that we're moving the responsibility to the command, getting it out from Sync. I'll let this bug live for this.

- Work with uploading: I need to see if can refactor the "uploading" attribute to be hold on each command and not depend of a global structure. I still need to do this analysis.

- Remove from the list in several places: A refactor needs to be done in the Command steps through its life. For this, bug #704473 is open.

[Facundo Batista (facundo)]

This is more complex than just moving the cancel out of Sync. Some cancel_upload must still live in Sync (and maybe Unlink be able to cancel Uploads/Downloads).

For cancel_download is even more complicated, we may finish moving the create_partial/remove_partial from Sync to Download.

In any case, we'll not do this for Natty