recursive_isinstance(), recursive_issubclass(): New code here returned

NULL in case of error, but the functions are declared to return int.
MSVC 6 properly complains about that.  Return -1 on error instead.

Objects/abstract.c

@@ -2033,7 +2033,7 @@ recursive_isinstance(PyObject *inst, PyObject *cls, int recursion_depth)
                 if (!recursion_depth) {
                     PyErr_SetString(PyExc_RuntimeError,
                                     "nest level of tuple too deep");
-                    return NULL;
+                    return -1;
                 }
 
 		n = PyTuple_GET_SIZE(cls);
@@ -2088,7 +2088,7 @@ recursive_issubclass(PyObject *derived, PyObject *cls, int recursion_depth)
                         if (!recursion_depth) {
                             PyErr_SetString(PyExc_RuntimeError,
                                             "nest level of tuple too deep");
-                            return NULL;
+                            return -1;
                         }
 			for (i = 0; i < n; ++i) {
 				retval = recursive_issubclass(