Cannot send backspace using IBus' forward_key_event

[Trung Ngô]

I'm trying to eleminate the use of pre-editing in my input method. In order to do so, I have to send fake backspace events to manipulate the text buffer. Unity is the only application I've tried where this approach doesn't work.

In my IBus engine, I'd use this call to send a fake backspace:

    self.forward_key_event(IBus.BackSpace, 14, 0)

Attached is a minimal program to test this bug. It needs `python-gi`, `gir1.2-ibus` and `ibus` running to work. How to test:

1. Open gedit, type something.
2. Run the script `python ibus_template.py`
3. Press any key in gedit. With each keypress, a character will be removed from gedit's buffer.
4. Repeat with Unity's Dash