[racket] online check syntax error display tweak

At Fri, 9 Sep 2011 10:58:23 -0500,
Robby Findler wrote:
> I thought about that, but I didn't want it to overlap the text and I
> didn't want it to slide everything over to make space.

What about horizontal lines before and after the relevant line,
running across the whole editor. Finding the relevant code becomes a
matter of following the lines. Grant Rettke's IntelliJ screenshot does
something similar, and I think it helps.

> What if there was a keybinding that jumped you to the right place?

That would be great too. Emacs uses C-x ` for that.

Vincent