Fix a warning with MSVC Premium 2013

Reported by Ron Britvich.

No functional change.
Revert "Score extractors"

Are broken for big-endian case and
I have verified with MSVC 2013 Premium
bench is correct and there is no
miscompilation, so the main reason
to change the original code drops.

No functional change.
Move Tempo to evaluation

No functional change.
Avoid to use nullChild

Should be a non functional change, but
for some reason bench is changed.

bench: 8454456
Temporary revert previous patch

Split previous patch in 2 steps: first remove
the MOVE_NULL hack, then retire nullChild.

The first step is a prerequisite
for second one and affects bench.

The second step (next patch) just removes nullChild
without affecting bench.

bench: 8205159
Remove 'update gains' hack

Use (move != MOVE_NONE) condition to
filtering out updating gains at root.

bench: 8454456
Avoid to use nullChild

Use instead:

(ss-1)->currentMove == MOVE_NULL

No functional change.