simplification in gen_quiet_checks()
only set ep square when it can be attacked by enemy pawns (6463840)
adjust mate scores before storing in TT (6227306)
TT scores must be adjusted, and search scores must also be adjusted to be relative to the current position before storing in TT. Difference in bench is only 1 node, and it's a logical bugfix, so skip testing (save some electricity).
Spotted by Marco Costalba.
Merge branch 'master' into tt_adjust (6463841)