Automatic Ko detection

[billstclair]

If, on his first move of this turn, a player has no sequence of moves that end up in a novel position, there is currently no way for him to end his turn and force the other player to make a sequence of moves that DOES end up in a novel position. That's because I was afraid of the combinatorial explosion to determine it.

There is NO combinatorial explosion. You have to try at most the number of position that are in GameState.history list, which isn't many.

[billstclair]

I've done this, but there's a bug.

Starting from the position below, white has two moves. Both end in "Other Ko" on the "End Turn" button. Both say in the message that white may click the "End Turn" button. Right behavior. Wrong message.

["BP","CA",true,null,null,["----w-------------S-----O-------T----------------","HSMTW---------","cmcghg--------"],["----w-------------S-----O-------T----------------"],[]]

[billstclair]

I think my last commit fixed this: e0e1cb4