FIX: ROUND/EVEN/TO differences from Rebol2

fixes: metaeducation/rebol-issues#2323

DTOA was used in mode without limiting number of digits. Now it uses `system/options/decimal-digits` value for number of maximal displayed digits.

Author: Oldes

src/core/f-math.c

@@ -253,7 +253,7 @@
 	if (decimal_digits < MIN_DIGITS) decimal_digits = MIN_DIGITS;
 	else if (decimal_digits > MAX_DIGITS) decimal_digits = MAX_DIGITS;
 
-	sig = (REBYTE *) dtoa (d, 0, decimal_digits, &e, &sgn, (char **) &rve);
+	sig = (REBYTE *) dtoa (d, 2, decimal_digits, &e, &sgn, (char **) &rve);
 
 	digits_obtained = rve - sig;