[racket] Sandboxed evaluation with 2htdp/image requires

At Sun, 5 Feb 2012 10:35:47 -0700, Matthew Flatt wrote:
> The decision of whether `racket/gui/base' is available is made through
> `gui-available?'. That the check happens once at the top level of
> `racket/sandbox', which unfortunately makes it sensitive to the order
> of modules in the program that creates sandboxes.
> 
> [...]
>
> We should look into fixing the sandbox so that the choice of GUI or not
> is made later,

I've pushed that change to the repo.