[racket] Embedded Racket 5.1.3 on Windows

Another question. It looks like scheme_set_stack_base is not working
with CGC 5.0.x and 5.1.x. as it used to be with previous versions. Is
it not supported anymore? If so it might be worth updating the
documentation.

#include <scheme.h>

static __declspec(thread) void *tls_space;

int main()
{
   int dummy = 0;
   scheme_register_tls_space(&tls_space, 0);
   scheme_set_stack_base(&dummy, 1); // access violation
   //scheme_set_stack_base(&dummy, 1); // ok with 5.0.1 but crashes with 5.1.3
   return 0;
}