Prune more moves after a null search because of
a lower beta limit then in main search.
In test positions reduces the searched nodes of 30% !!!!
Signed-off-by: Marco Costalba <mcostalba@gmail.com>
There are subtle differences in the king evaluation
that should be clear to avoid misunderstandings.
Signed-off-by: Marco Costalba <mcostalba@gmail.com>