Fix bug in unsigned 32-bit division and remainder routines, which could cause mis-evaluation of constant expressions.

The following example shows cases that were mis-evaluated:

/* Should print "3 10000" */
#include <stdio.h>
int main(void)
{
	printf("%lu %lu\n", 100000ul / 30000ul, 100000ul % 30000ul);
}

Expression.asm

@@ -90,7 +90,7 @@ dv3      asl   ans                      roll up the next number
          rol   ans+6
          sec                            subtract for this digit
          lda   ans+4
-         sbc   num1
+         sbc   num2
          tax
          lda   ans+6
          sbc   num2+2
@@ -267,7 +267,7 @@ dv3      asl   ans                      roll up the next number
          rol   ans+6
          sec                            subtract for this digit
          lda   ans+4
-         sbc   num1
+         sbc   num2
          tax
          lda   ans+6
          sbc   num2+2