Issue 3611: in some cases (a __del__ re-raising an exception, when called from inside an 'except' clause), the exception __context__ would be reset to None. This crases the interpreter if this precisely happens inside PyErr_SetObject. - now the __context__ is properly preserved - in any case, PyErr_SetObject now saves the current exc_value in a local variable, to avoid such crashes in the future. Reviewer: Antoine Pitrou.