Rich comparisons fallout: instance_hash() should check for both

__cmp__ and __eq__ absent before deciding to do a quickie
based on the object address.  (Tim Peters discovered this.)

Objects/classobject.c

@@ -762,14 +762,20 @@ instance_hash(PyInstanceObject *inst)
 	PyObject *func;
 	PyObject *res;
 	long outcome;
-	static PyObject *hashstr, *cmpstr;
+	static PyObject *hashstr, *eqstr, *cmpstr;
 
 	if (hashstr == NULL)
 		hashstr = PyString_InternFromString("__hash__");
 	func = instance_getattr(inst, hashstr);
 	if (func == NULL) {
-		/* If there is no __cmp__ method, we hash on the address.
-		   If a __cmp__ method exists, there must be a __hash__. */
+		/* If there is no __eq__ and no __cmp__ method, we hash on the
+		   address.  If an __eq__ or __cmp__ method exists, there must
+		   be a __hash__. */
+		PyErr_Clear();
+		if (eqstr == NULL)
+			eqstr = PyString_InternFromString("__eq__");
+		func = instance_getattr(inst, eqstr);
+		if (func == NULL) {
 			PyErr_Clear();
 			if (cmpstr == NULL)
 				cmpstr = PyString_InternFromString("__cmp__");
@@ -778,6 +784,7 @@ instance_hash(PyInstanceObject *inst)
 				PyErr_Clear();
 				return _Py_HashPointer(inst);
 			}
+		}
 		PyErr_SetString(PyExc_TypeError, "unhashable instance");
 		return -1;
 	}