proposal: handle middle/right clicks on arrows of scrollbarsdifferently

[Vlad Harchev <hvv hippo ru>]

 Hi,

 I think from GUI usability standpoint, it would be nice to extend the
handling of right/middle clicks on scrollbar's arrows (that are in the edges)
1) Middle or right click on the arrow moves the slider right to that edge of
	scrollbar
2) Even more inteligent:
   Middle click on the arrow moves the slider right to that edge of
   scrollbar, right click - right to oposite edge. This is IMO very handy
   when your pointer is over the left arrow of horizontal scrollbar and you
   have to scroll to 90% of scrollbar: you press right button (slider goes to 
   the 100% limit), and then press left mouse button several times (it's
   over left arrow, remember?) to move slider to 90%.
   May be the meaning of right and middle presses should be reversed since
   middle button is not present on a lot of mouses.

 Sorry, I don't have time to dig in the gtk sources and understand it to make
a correct patch. But it seems it would be very easy to code it.
 What do you think about this?

 Best regards,
  -Vlad