Alexander, I think it should be as simple as replacing the if (!PyInt_Check(ilow) && ...) block with something like this:

	if (!PyInt_Check(ilow) && !PyLong_Check(ilow)) {
		PyNumberMethods *nb = Py_TYPE(ilow)->tp_as_number;
		PyObject *temp;
		if (PyFloat_Check(ilow) || nb == NULL || nb->nb_int == NULL) {
			PyErr_Format(PyExc_TypeError,
				     "range() integer start argument expected, got %s.",
				     ilow->ob_type->tp_name);
			goto Fail;
		}
		temp = (*nb->nb_int)(ilow);
		Py_DECREF(ilow);
		ilow = temp;
		if (temp == NULL)
			goto Fail;
	}

and then doing the same for the ihigh and istep blocks.  But I haven't tested this.

Mark