[computer-go] incremental liberty counts

[Rémi Coulom]

Don Dailey wrote:
> It takes approximately 25% of the time to see if something gets
> captured.   That routine stops as soon as it notices the target group is
> safe, but it still has to repair the flag bit for those points it has
> already visited.   It's actually a very simple routine but it does a lot
> of work.
>   
The GNU-Go mark trick I rapidly explained in a previous mail saves the 
effort of repairing a flag bit for visited points (or strings). You may 
have good reasons not to use it, but I thought I'd repeat this just in 
case it was not clear the first time I wrote it (which is very likely 
since my explaination was very short).

Rémi