Update bestValue when futility pruning (2)

Same idea of 5af8179647b9e80353c
in qsearch() but applied to search()

After 15500 games at 15+0.05
ELO: 4.48 +-3.4 (95%) LOS: 99.5%
Total: 15500 W: 3061 L: 2861 D: 9578

bench: 4985829
Raise Min Split Depth

Raise the limit to 12 so to allow people to test
on many cores machines.

Suggested by Gary and Martin.

No functional change.
Merge branch 'master' into qs_no_recaptures