add warning for mismatching mate scores

[robertnurnberg]

This PR emits a warning if both engines claim to have found a proven win, and same for a proven loss. Of course, this can only happen if one of the two engines is buggy, or if the first engine sent a bestmove that does not correspond to the (winning) mate score.

I prefixed the warning line that contains both info lines with Infos;. Let me know if this should be changed.

Example:

Warning; Sign mismatch in mate scores 3 and 27 from sf-dev and winter
Infos; info depth 13 seldepth 6 multipv 1 score mate 3 nodes 2187 nps 1093500 hashfull 1 tbhits 0 time 2 pv d2c2 c7b8 e6d6 b8b7 e2f3 ; info depth 6 seldepth 12 time 17 nodes 4512 nps 250666 score mate 27 wdl 0 0 1000 pv c7b7 e2f3 b7b8 e6e5
Position; fen rnb1kbnr/ppp1pppp/8/4q3/8/2N5/PPPP1PPP/R1BQKBNR w KQkq - 2 4
Moves; g1e2 g8f6 d2d4 e5a5 c1d2 b8c6 a2a3 h7h5 e2g1 a5b6 d4d5 f6g4 g1h3 c6d4 f1d3 g4e5 d2e3 c7c5 d5c6 e5c6 h3g5 c8g4 d1b1 a8d8 b1a2 e7e6 h2h3 f8c5 h3g4 d4c2 d3c2 c5e3 g5e4 e3f2 e4f2 b6e3 c3e2 c6d4 c2d3 d4e2 d3e2 d8d2 a2c4 f7f5 h1h3 d2b2 h3e3 b7b5 c4e6 e8d8 a1d1 b2d2 d1d2 d8c7 d2c2 c7b7