Revert to Galurung's KBPsK endgame

After reverting to the original Tord's
endgame, a search on position

7k/6p1/6B1/5K1P/8/8/8/8 w - - 0 1

Reports, correctly, a draw score instead of
an advantage for white.

Issue reported by Uri Blass.

bench: 8678654
maxply unleashed
Add stealmate detection to evaluation

Currently a stealmate position is misevaluated
in a negative/positive score, this leads qsearch(),
that does not detects stealmates too, to return the
wrong score and this yields to some kind of endgames
to be completely misevaluated.

With this patch is fully fixed follwing position

7k/6p1/6B1/5K1P/8/8/8/8 w - - 0 1

Also in SMP case.

Correct root cause analysys by Ronald de Man.

bench: 8678654
Fully correct stealmate detection

In the (rare) cases when the two conditions
are true, then fully check again with a slow
but correct MoveList<LEGAL>(pos).size().

This is able to detect false positives like
this one:

8/8/8/Q7/5k1p/5P2/4KP2/8 b - - 0 17

When we have a possible simple pawn push that
is not stored in attacks[] array. Because the
third condition triggers very rarely, even if
it is slow, it does not alters in a measurable
way the average speed of the engine.

bench: 8678654
Merge branch 'master' into correctmate
back abs for tt