[racket-dev] teaching language error messages

I see that the teaching language error messages now have things like
this in them (where the . is an image literal):

Welcome to DrRacket, version 5.1.2.3--2011-07-19(4b77a0fc/d) [3m].
Language: Beginning Student; memory limit: 128 MB.
> (+ 1 (list .))
+: expects a number as 2nd argument, given (cons an image empty)
I see that this is being done via regexps on the error message
strings. This seems bad.

Can we at least get some delimiters on there so it doesn't look like a
malformed use of 'cons'?

Robby