Issue 3051: Let heapq work with either __lt__ or __le__.

Modules/_heapqmodule.c

@@ -17,13 +17,12 @@ static int
 cmp_lt(PyObject *x, PyObject *y)
 {
 	int cmp;
-	cmp = PyObject_RichCompareBool(x, y, Py_LT);
-	if (cmp == -1 && PyErr_ExceptionMatches(PyExc_AttributeError)) {
-		PyErr_Clear();
+
+	if (PyObject_HasAttrString(x, "__lt__"))
+		return PyObject_RichCompareBool(x, y, Py_LT);
 	cmp = PyObject_RichCompareBool(y, x, Py_LE);
 	if (cmp != -1)
 		cmp = 1 - cmp;
-	}
 	return cmp;
 }