Provide the ability to integrate QTextEdit with an external undo/redo framework

It would be nice if there were a way to integrate an external undo/redo framework with QTextEdit. Currently, the undo/redo stack is managed internally, which makes it difficult to synchronize its changes with a general undo/redo manager.

Update: the undoCommandAdded() has been added to QTextDocument in 4.4. This should be sufficient for synchronizing QTextEdit's undo/redo actions with a general undo/redo manager.