Can't add a stone after having removed it in edit mode

[omidmnz]

I'm using qgo 2.1.0 on a 64bit Archlinux machine, installed from the community repository. To reproduce:

1. Start a new game, with no players being computer.
2. Go to edit mode.
3. Choose the "Stone" tool (with a plus sign) under "Stone tools"
4. Add a stone, e.g. a black stone, with left click.
5. Left click again, to remove the stone.
6. Now try adding another stone in the same place, with either left or right click. It doesn't add anything.

One can add stones in that place in game mode, or having the stone tool disabled, but with the stone tool, nothing seems to change the behavior.

[pzorin]

Editing is more or less broken by design, and I haven't seriously attempted fixing it, mostly because I don't know how it should interact with the game tree. It is probably a good idea to follow the SGF standard and make each move contain either one actual move or an arbitrary number of stone edits. Unfortunately, right now I don't have time to work this out.