rook open file bonus
signature = 7413073
rook open bonus adjustment
increase a little, also reduce the value of a rook to compensate the biais (actually a bit more while at it).
signature = 7470533
improve readme and comment History+Refutation
No functional change.
fix error in copyright header
no abortion before iteration 1 is finished
In extreme cases, like very low fixed nodes search in certain positions, the search limits could trigger a search abortion before iteration 1 is finished. This is a disaster, as the best move could either be null or completely stupid.

Also increase the node polling resolution. Now the search limits are checked every 256 nodes, instead of 1024. With this patch, the 'nodes' feature can be used reliably as a strength limitation feature.

No functional change.