Polishing the icon stretching code

[Matthias Clasen <mclasen redhat com>]

I have attached a patch to
http://bugzilla.gnome.org/show_bug.cgi?id=157271
which makes nautilus use the resize cursors when stretching 
an icon. It also makes the knob image themable. 

There are some more things which could be improved here:

 - Add keynav for stretching icons (proposal: use Ctrl-+/-  to
   stretch the icon while the stretch handles are displayed)
 - Don't hardcode a line width of 1 for the focus-like rectangle
   drawn with the stretch handles, but use a value derived from
   focus-width.

 I also note that "note-indicator.png" is another icon that should
 probably be made themable.


Matthias