Smarter improvement of lunch attacks.

[gunnar]

The function improve_lunch_attack() tries to avoid capturing single or double stones on the first line with a first line hane since that can cause false eyes. E.g. playing to the left of the two black stones on the first line here,

and instead moves the attack move up to the second line if that's also an attack point.

However, this can become extremely silly in positions like

where moving a move directly to the right of the black stone on the first line up to the second line makes absolutely no sense at all.

The attached patch should amend this problem.

[gunnar]

Revision of improve_lunch_attack().

[gunnar]

No unpleasent surprises in the regressions. Only one good PASS and a modest reduction of owl nodes.

trevorc:820     PASS A6 [A6]
1 PASS
Total nodes: 1700585382 3337679 12402666 (-0.051% -0.18% -0.013%)