Entering a pawn endgame is no more dangerous

A simplification of the 'dangerous' definition.

Seems neutral at reverse test at long TC

master vs patch
LLR: -2.96 (-2.94,2.94)
Total: 16974 W: 3122 L: 3139 D: 10713

bench: 4689029
Revert "Remove confusing optimization"

This reverts commit e05c80a08859f6c4f0f599ca0b262ced00ad66fe.

we gain a speed up of 1.5% under gcc !

No functional change.
Merge branch 'master' into pa_gtb