[plt-scheme] Unicode strings in mzscheme

Hi,

How do I get unicode working (or at least, working as I would expect - I guess
it probably works already!) in MzScheme.  In DrScheme, string-ref returns a
reasonable value for an accented letter but MzScheme behaves differently.

This is DrScheme:

(display "más")
(newline)

(string-ref "más" 1)

And the result:

Welcome to DrScheme, version 360.
Language: Pretty Big (includes MrEd and Advanced Student).
más
#\á

And this is MzScheme:

C:\>mzscheme
Welcome to MzScheme version 360, Copyright (c) 2004-2006 PLT Scheme Inc.
> (string-ref "más" 1)
#\?

Thanks,

Ian