[racket] using scribble's evaluator for planet packages

>
>  format-output: missing output, possibly from a sandbox without a
>  configured `sandbox-output'
>
> I'm not happy with it -- the "format-output: ..." seems like it's too
> easy to translate to "probably some internal bug, not my problem".
>
> Any suggestions for a better message?

I can't think of an improved text for it.  The message, at the very
least, gives something to search with Google.

I think it would help a bit to add an example in the Scribble
documentation that uses make-evaluator in the context of Scribble.
I'll send you a patch to show what I mean.