Use ALL_PIECES value to reference attackedBy

No functional change
Fix bogus mate scores in some positions

Always before pruning the move, it's important to check that:

bestValue > VALUE_MATED_IN_MAX_PLY

See example position:

8/2p1p3/P1NpP3/3k4/1P1BN3/2P1P3/2Q5/6K1 w - - 0 1
http://support.stockfishchess.org/discussions/problems/268-wrong-declaring-a-forced-mate-in-3-moves

This problem was present in 2.3.1, then it was fixed by my patch.

After 24000 games at 15+0.05
ELO: 2.40 +-4.4 (95%) LOS: 95.7%
Total: 24000 W: 4774 L: 4608 D: 14618

bench: 4465997
Passed pawn evaluation change

From the position referenced in Gary's KNPKB endgame change it appears
to me that we overvalue passed pawns that can't promote due to
attackers.

This version appears to hold it's strength (approx +7 ELO) in tests at
5s, 15s and 60s in 1000 game tests.
Currently testing at 60s+0.05 with 4GB hash tables

Signed-off-by: Marco Costalba <mcostalba@gmail.com>
Merge branch 'master' into passed_pawns