further improvements

project/keyframe.cpp

@@ -38,7 +38,7 @@ void delete_keyframes(QVector<EffectField *>& selected_key_fields, QVector<int>
 		for (int i=0;i<key_indices.size();i++) {
 			ca->append(new KeyframeDelete(fields.at(i), key_indices.at(i)));
 		}
-		undo_stack.push(ca);
+		Olive::UndoStack.push(ca);
 		selected_keys.clear();
 		selected_key_fields.clear();
 		update_ui(false);