Make verification search more accurate.
Now following position gets solved at depth 79, while
verification search is still noticeably reduced.

8/8/8/2p5/1pp5/brpp4/1pprp2P/qnkbK3 w - - 0 1
info depth 79 seldepth 30 score mate 15 nodes 5672950 nps 2511266 time 2259 multipv 1 pv h2h3 a1a2 h3h4 a2a1 h4h5 a1a2 h5h6 a2a1 h6h7 a1a2 h7h8n a2a1 h8g6 a1a2 g6e5 a2a1 e5d7 a1a2 d7c5 a2a1 c5d7 a1a2 d7e5 a2a1 e5c4 a1a2 c4a5 a2a1 a5b3

bench: 7430277