Theme progress indicator & cursor

AHAH framework is a great module, but the visual effects are not easy to customize.

It should be possible to replace the progress indicator with a different graphic and control where it would appear. Right now ahah_forms.js inserts the indicator before wrapper and it may not the rest of the design. The wishlist of improvements:

1) Allow picking a different progressbar image
2) Account for variable image size in ahah_forms.js (now in var wait_image_size)
3) Assign a CSS class to pre-pended progressbar DIV
4) Consider [optional] emptying of the wrapper before the callback responded (replace with progressbar)
5) Allow customization of the mouse cursor while AHAH request in progress (now the clock, should be regular cursor)

That's it for now.