More aggressive post-futility pruning
Fix potential overflow
Merge Joona's increased static null pruning

The idea is to fail high more easily in static
null test if in the parent node we are already
very deep in the move list, so the propability
to fail high there is very low.

[edit: I have slightly changed the functionality
moving

ss->futilityMoveCount = moveCount;

At the end of the pruning code, this should not affect
ELO in anyway, but makes code more natural and logic]

Test with SPRT is good at 15+0.05
LLR: 2.96 (-2.94,2.94)
Total: 50653 W: 10024 L: 9780 D: 30849

And at 60+0.05
LLR: 2.97 (-2.94,2.94)
Total: 40799 W: 7227 L: 6921 D: 26651

bench: 4530093
Increase rook/queen on 7th bonus

Shows an increase at 15+0.05
LLR: 3.01 (-2.94,2.94)
Total: 20450 W: 4091 L: 3927 D: 12432

And at 60+0.05
LLR: 2.97 (-2.94,2.94)
Total: 61432 W: 10849 L: 10441 D: 40142

bench: 4493356

Signed-off-by: Marco Costalba <mcostalba@gmail.com>