When an unhandled exception happens, report the repr() of the function

that was used to start the thread.  This is useful to track down the
source of the problem when there is no traceback, as can happen when a
daemon thread gets to run after Python is finialized (a new kind of
event, somehow this is now possible due to changes in Py_Finalize()).

Modules/threadmodule.c

@@ -179,20 +179,28 @@ t_bootstrap(void *boot_raw)
 	PyEval_AcquireThread(tstate);
 	res = PyEval_CallObjectWithKeywords(
 		boot->func, boot->args, boot->keyw);
-	Py_DECREF(boot->func);
-	Py_DECREF(boot->args);
-	Py_XDECREF(boot->keyw);
-	PyMem_DEL(boot_raw);
 	if (res == NULL) {
 		if (PyErr_ExceptionMatches(PyExc_SystemExit))
 			PyErr_Clear();
 		else {
-			PySys_WriteStderr("Unhandled exception in thread:\n");
+			PyObject *file;
+			PySys_WriteStderr(
+				"Unhandled exception in thread started by ");
+			file = PySys_GetObject("stderr");
+			if (file)
+				PyFile_WriteObject(boot->func, file, 0);
+			else
+				PyObject_Print(boot->func, stderr, 0);
+			PySys_WriteStderr("\n");
 			PyErr_PrintEx(0);
 		}
 	}
 	else
 		Py_DECREF(res);
+	Py_DECREF(boot->func);
+	Py_DECREF(boot->args);
+	Py_XDECREF(boot->keyw);
+	PyMem_DEL(boot_raw);
 	PyThreadState_Clear(tstate);
 	PyThreadState_DeleteCurrent();
 	PyThread_exit_thread();