* Use realmd for domain joining and lookup, runtime dependency
* Validate join domain correctly
* Add UmRealmManager for handling some stuff above the autogenerated
realmd dbus code
* Show a dialog if the user's credentials cannot be used to join
the domain. Prompt for admin creds.
* Register the user's login with the AccountsService
* This depends on the CacheUser() method of AccountsService
https://bugzilla.gnome.org/show_bug.cgi?id=677548
The don't really make sense in GDM anymore since all the tools
that used them have been removed from there. It makes more sense
for them to live close the UI that selects and manipulates them.
At some point we should probably consider making face images themeable
so that they can be loaded in various sizes.
