Revert back KBPsK to latest Gary's version

The bug was found to be elsewhere. This version
is correct and also is able to detect as draw
positions like:

8/8/5b2/8/8/4k1p1/6P1/5K2 b - - 6 133

bench: 8678654
Revert stalemate detection in evaluation

Unfortunatly we have a slow down that causes
a regression in STC with no-regression mode:

LLR: -2.96 (-2.94,2.94) [-3.00,1.00]
Total: 22454 W: 3836 L: 4029 D: 14589

bench: 8678654
Revert dynamic contempt

On a final fixed game number test it failed
to prove better than standard version.

STC 15+0.05

ELO: -0.86 +-1.7 (95%) LOS: 15.8%
Total: 57578 W: 10070 L: 10213 D: 37295

bench: 8802105
Change search() signature

Pass SpNode as template parameter.

No functional change.
Rewrite Score extractors

Less tricky and even a bit faster. With this
version Visual Studio Ultimate 2013 Update 2 RC
runs fine even in O2 optimization.

No functional change.
Allow a slave to 'late join' another splitpoint

Instead of waiting to be allocated, actively search
for another split point to join when finishes its
search. Also modify split conditions.

This patch has been tested with 7 threads SMP and
passed both STC:

LLR: 2.97 (-2.94,2.94) [-1.50,4.50]
Total: 2885 W: 519 L: 410 D: 1956

And a reduced-LTC at  25+0.05
LLR: 2.95 (-2.94,2.94) [0.00,6.00]
Total: 4401 W: 684 L: 566 D: 3151

Was then retested against regression in 3 thread case
at standard LTC of  60+0.05:

LLR: 2.96 (-2.94,2.94) [-4.00,0.00]
Total: 40809 W: 5446 L: 5406 D: 29957

bench: 8802105
Reformat and simplify previous patch

No functional change.
Clarify some comments in SMP code

Spotted by Joona.

No functional change.
Pass Position as const ref in update_stats()

No functional change.