[racket] scribble formatting tweak?

I've pushed this change to the git repo.

At Tue, 12 Jun 2012 22:02:26 -0400, Neil Van Dyke wrote:
> With Scribble-formatted API documentation, one thing I kinda miss from 
> Lisp-y manuals (such as those formatted by Texinfo, or CLtL2) is a 
> better cue that something is documenting, say, a procedure, rather than 
> syntax, rather than a parameter.
> 
> One way to do this with Scribble would be to subtly add a label to the 
> light blue background for definition syntax synopses.  For example 
> (click the second thumbnail): http://imgur.com/a/xFTFn
> 
> Of course, with this particular format, the definition could obscure 
> this label, so unless you wanted to make the label a really big font 
> that was intended to be obscured (which doesn't really fit the look of 
> the manuals), it would complicate formatting.
> 
> Or you could put the label in the right margin, where footnotes go, but 
> I'd actually like to get rid of the right margin as a necessary thing 
> later, and turning footnotes into hover slide-outs when there isn't 
> enough horizontal room, so I'm not fond of putting anything new in the 
> margins that we'd want visible as cues.
> 
> Comments?
> 
> Neil V.
> 
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