Mark: would it be possible to keep the "2 digits" hack in 
PyLong_FromLong, especially with base 2^15? Eg. "#if PyLong_SHIFT == 
15". The base 2^15 slow, so don't make it slower :-)

-	/* 2 digits */
-	if (!(ival >> 2*PyLong_SHIFT)) {
-		v = _PyLong_New(2);
-		if (v) {
-			Py_SIZE(v) = 2*sign;
-			v->ob_digit[0] = (digit)ival & PyLong_MASK;
-			v->ob_digit[1] = ival >> PyLong_SHIFT;
-		}
-		return (PyObject*)v;
-	}