add a special Provides: to all login manager packages

[Kevin Kofler]

Colin Walters wrote:
> I don't think it's as obvious as that; both XFCE and LXDE share a lot
> of the same infrastructure that's used for gdm (primarily GTK+).  What
> exactly about GDM is not suitable?  That's the question they should be
> able to answer.

The latest GDM drags in a metric buttload of GNOME infrastructure, in
particular gnome-session, which drags in control-center, which drags in
pretty much all of GNOME, including metacity, libcanberra, several
libgnome* etc.

The days where GDM only needed GTK+ are long gone.

        Kevin Kofler