[plt-scheme] v299 unicode -> (char *)

I'm porting an extension from v208 to v299.  Sorry, if this is dumb
question, but when scheme passes my extension a string, how do I get
a (char *) from the unicode (Scheme_Object *).  In the old days I just
SCHEME_STR_VAL(argv[0]).  SCHEME_CHAR_STR_VAL doesn't do it, it extracts
a (mzchar *).  SCHEME_BYTE_STR_VAL might do it, but then I would need
to convert from chars to bytes in scheme (I guess) before calling the
extension?

Thanks,

Ron StillInAscii
stanonik at cogsci.ucsd.edu