score calculation

[sedire]

Hi! Thanks a lot for a great implementation.
While playing around with it, I noticed some strange behavior when score is calculated.
In the score() method of Position class:

while True:
i = self.board.find('.', i+1)

shouldn't it be board.find instead of self.board.find? Or I misunderstood something about go rules?
The way it is now, floodfill will not only be filling '.' fields, but also the others during score calculation.