Patch for deleting tiles when commands are deleted from the undo stack

[LukasT.dev@gmail.com]

On Saturday 20 March 2010 17:09:28 Cyrille Berger wrote:
> On Saturday 20 March 2010, Boudewijn Rempt wrote:
> > On Friday 19 March 2010, Boudewijn Rempt wrote:
> > > Sure!
> > 
> > It seems to work now -- I haven't got new regressions indeed.
> 

> I actually noticed some problem with undoing with disappearing tiles.

I don't have your patch, but I have this bug also.
Sometimes reproducible like: 

* start with white template any size,  
* paint one stroke left, one stroke right, one stroke right, one stroke up, 
one stroke down with some paintops (prefer mine, so that I could include your 
art in my thesis if it is nice) 
* undo til you want to return to white canvas, bah, canvas is transparent.
* btw you could do random strokes

So not your mistake most probably