Allow background drawing on a Space-specific basis.

I use four Spaces, for writing, communications, a place to shove stuff with long progress bars, and everything else. I'd like to have the former three Spaces set to static pictures with opaque menubars, and have my primary Space still rotate from my Flagged iPhoto pictures. If you could either implement random desktop images or Space-specific background drawing.

In the meantime I'll just use background colors, which don't require the image drawing to be on.