debcheckout for package with Ubuntu changes and without Vcs fields should suggest udd branch

When using debcheckout for package with Ubuntu changes and without Vcs fields, it might be helpful for it to suggest or even automatically use the udd branch.

Here's what currently happens:

$ apt-cache policy indicator-weather | grep "Installed"
  Installed: 11.05.31-0ubuntu1
$ debcheckout indicator-weather
No repository found for package indicator-weather.

A Vcs-* field is missing in its source record. See Debian Developer's
Reference 6.2.5:
 `http://www.debian.org/doc/developers-reference/best-pkging-practices.html#bpp-vcs'
If you know that the package is maintained via a version control
system consider asking the maintainer to expose such information.

Nevertheless, you can get the sources of package indicator-weather
from the Debian archive executing:

 apt-get source indicator-weather

Note however that what you obtain will *not* be a local copy of
some version control system: your changes will not be preserved
and it will not be possible to commit them directly.