pyWallpaper Updated

I have committed a much more comprehensive version of pyWallpaper to the subversion repository.

It is multi-threaded to speed up the wallpaper construction  (most of the threads end up being I/O bound, so this is a win in terms of elapsed time).

Also supports walking subfolders by prefixing paths with a +

The code is still available at http://code.google.com/p/pywallpaper/