Icons not appearing for SelectManyShuttle

[Jeantine Mankelow]

We have just started using the selectManyShuttle component, but the 
move/move-all/remove/remove-all icons are not showing up.

I had a go at debugging it and I can see that NullIcons are getting 
returned. It seems our skin is pointing to the minimal-desktop.xss, 
however I can't see any entry in this file for the shuttle component, 
nor in any of the other xss files in the same directory in the jar.  Any 
ideas why this doesn't work? 

Alternatively could someone tell me how I can extend the skin, so we can 
add our own icons for this component.

Thanks,
Jeantine