Comment 24 for bug 844081

Correct on seamlessness being the goal. The only thing that has to work for 12.04 is that the greeter should layout the wallpaper using the same transformation as the GNOME/Unity default. Anything else is a bonus, and worth bumping to a later release. I don't think we want to support transitioning wallpapers at all, if someone has this configured we should just show the first one (transitioning would be confusing and look like the selected user was changing). Treat a non image based wallpaper as unset and show the system default for now.