defdict_reduce(): Plug leaks.

We didn't notice these before because test_defaultdict didn't
actually do anything before Georg fixed that earlier today.
Neal's next refleak run then showed test_defaultdict leaking
9 references on each run.  That's repaired by this checkin.

Modules/collectionsmodule.c

@@ -1117,7 +1117,7 @@ defdict_copy(defdictobject *dd)
 static PyObject *
 defdict_reduce(defdictobject *dd)
 {
-	/* __reduce__ must returns a 5-tuple as follows:
+	/* __reduce__ must return a 5-tuple as follows:
 
 	   - factory function
 	   - tuple of args for the factory function
@@ -1155,6 +1155,7 @@ defdict_reduce(defdictobject *dd)
 	}
 	result = PyTuple_Pack(5, dd->dict.ob_type, args,
 			      Py_None, Py_None, items);
+	Py_DECREF(items);
 	Py_DECREF(args);
 	return result;
 }