A simple hack to generate a transitioning background for a Gnome
desktop and automagically update your user preferences with the
result.  You stick the pics you want in a folder, point this at it,
and away you go.
                                                                                                       
You could use icron if you want it to auto-update.

Copyright (c) 2009-2012 Rodger Donaldson.  Consider this under the
2-clause BSD license.

Format is derived from this article:
 http://www.linuxjournal.com/content/create-custom-transitioning-background-your-gnome-228-desktop

The "XML" that ships with common GNOME distros for this aren't actual
XML because apparently in GNOME-land you bloat everything out with
psuedo-XML that doesn't actually parse as XML because...
                                                                                                       
This is the kind of thought-process that leads to GNOME 3 and GNOME
Shell.