Bug#168601: Resurrecting this bug

[David Nusinow <david_nusinow@verizon.net>]

retitle 168601 xdm: Provide a none option during dm selection question
thanks

I'm resurrecting this bug because I think the users could definitely use it
and it should be trivial to implement. We can deploy the code first in xdm
and provide it for the other dm's to add as well. The title reflects the
proper solution: provide an option in the list of dm's to select from for
"none". In #debian one of the common solutions is to do essentially this to
prevent any dm from starting up, and I think it'll be a great service to
the user to allow this. Removing the package is less optimal now that
aptitude is set to remove a whole metapackage (like x-window-system) if a
single component (like xdm) is removed so we want to provide an alternative
solution. This strikes me as the most elegant.

 - David Nusinow