gdm-config should set /apps/gdm/simple-greeter/disable_user_list

[broder]

This will, predictably, disable the user list that comes up and shows the recently logged in users.

Some brief notes from #369, which has some discussion relevant to this ticket:

I'm still trying to figure out how best to config-package-deverize the Gconf configuration necessary for setting disable_user_list. Options include transforming /var/lib/gdm/.gconf.path to add another source, or transforming /var/lib/gdm/.gconf.defaults directly. Of course, since /var/lib/gdm isn't world-readable, either mechanism is going to require a debathena-gdm-hack (a la cupsys-hack), which will suck.

[rbasch]

/var/lib/gdm/.gconf.path includes /etc/gconf/gconf.xml.system as a readonly source, so we could set it there via a postinst script.

[broder]

I really would much rather find a way to do the gconf config using config-package-dev instead of doing things in the postinst. Unlike with cluster-login-config, it's important that gdm-config uninstall itself cleanly.