Pending files from computers that have been removed from the account should be removed too

[Manuel Muradás]

  If a computer is disconnected while uploading a file, and then removed from the Ubuntu One account, the web interface still shows that file with the "uploading" status.

Steps to reproduce:
‣ In computer "A", copy a file ("big_file.avi") to Ubuntu One folder
‣ In computer "B", go to the web interface ("https://one.ubuntu.com/files/") and check until it appears (with the "uploading" status)
‣ Shutdown computer "A"
‣ In computer "B", remove computer "A" from the Ubuntu One account (in "https://one.ubuntu.com/account/machines/")

Expected behavior:
"big_file.avi" disappears from the web interface.

Observed behavior:
"big_file.avi" is still in the web interface, with the status "uploading".

Additional comments:
  I'm not sure if Ubuntu One reuses the token when re-pairing the computer to the account. In case it doesn't reuse it, or if computer "A" loses the token (reinstalling without backing-up Gnome's keyring) then the "uploading" files will stay there for ever (*).

(*) Workaround:
  First I thought that creating the same file in computer "B" doesn't solve the problem, but I made a typo, so:
‣ Create a file with the same name in computer "B" (an empty file is OK)
‣ Wait until the file is uploaded
‣ Delete it