[racket] line numbers in drracket

  I took a stab at adding line numbers to DrRacket. I started with this 
code from Grant Rettke: 
http://www.wisdomandwonder.com/link/1808/adding-a-gutter-to-drscheme 
which works reasonably well on its own but when I had trouble 
integrating it with DrRacket.

I think the way to go is to extend the definitions-canvas but the issue 
there is I can't seem to add new panel objects to the canvas. I can pass 
the definitions-text% straight through via (super-new [editor editor]). 
I tried making a proxy text%/editor-canvas% combo but I just had the 
same issue of not being able to add any elements to it.

So I guess the question is can I put more gui elements in a canvas?