Add a missing incref.

Backport candidate.
diff --git a/Modules/threadmodule.c b/Modules/threadmodule.c
index 245c51d..9818e4e 100644
--- a/Modules/threadmodule.c
+++ b/Modules/threadmodule.c
@@ -651,6 +651,7 @@
 	Py_INCREF(&Locktype);
 	PyDict_SetItemString(d, "LockType", (PyObject *)&Locktype);
 
+	Py_INCREF(&localtype);
         if (PyModule_AddObject(m, "_local", (PyObject *)&localtype) < 0)
         	return;