Check for an available slave early on

Don't take the split lock if we don't have
available slaves (about 30-40% of times).

This new condition allows to retire the now
redundant one on number of threads.

No functional change.
Small renaming in Tracing

No functional change.
Add bonus for advanced lever

Passed both STC
LLR: 2.95 (-2.94,2.94) [-1.50,4.50]
Total: 15413 W: 2670 L: 2530 D: 10213

And LTC:
LLR: 2.95 (-2.94,2.94) [1.00,6.00]
Total: 66908 W: 9398 L: 8960 D: 48550

Bench : 7859385
Tweak outpost name

This name is more accurate, since that function evaluates only one
outpost in every call.
No functional change.
Simplify pawn threats and merge into ThreatenedByPawn[]

Tested in no-regression mode,

passed STC
LLR: 2.96 (-2.94,2.94) [-3.00,1.00]
Total: 14477 W: 2493 L: 2362 D: 9622

and LTC
LLR: 2.95 (-2.94,2.94) [-3.00,1.00]
Total: 51964 W: 7091 L: 7013 D: 37860

bench: 7875814
Factor out pawn attacks in 'lever'

Improves readibility and possibly speed.

No functional change.
Triviality in UCI::loop

Code style paranoid in action here :-)

No functional change.
Fix a warning with MSVC in 'analyze' mode

Here MSVC is worried that

StepAttacksBB[PAWN][psq]

could overflow, so change psq initialization
to clarify psq is always less than 64.

No functional change.
Remove -ansi flag for Clang

It seems this flag is only for gcc and
yields a warning under OSX Mavericks:

clang: warning: argument unused during compilation: '-ansi'

No functional change.
Simplify unstoppable pawns

Tested in no-regression mode and passed both

STC
LLR: 2.95 (-2.94,2.94) [-3.00,1.00]
Total: 17919 W: 3103 L: 2978 D: 11838

and LTC
LLR: 2.96 (-2.94,2.94) [-3.00,1.00]
Total: 31460 W: 4414 L: 4308 D: 22738

bench: 7709279
Don't special case for abs(beta) >= VALUE_MATE_IN_MAX_PLY

Remove from the search this special case and apply
null search and razoring also in mate positions.

Tested in no-regression mode and passed both

STC
LLR: 2.96 (-2.94,2.94) [-3.00,1.00]
Total: 65431 W: 10860 L: 10810 D: 43761

and LTC
LLR: 2.95 (-2.94,2.94) [-3.00,1.00]
Total: 34928 W: 4814 L: 4713 D: 25401

This patch kicks in only in mate positions and in
these cases it seems beneficial in finding mates
faster as Yery Spark measured on the Chest mate suite:

Total number of positions 6425
Fixed nodes 200K per position

master: 1049
new:    1154

And also the 5446 'hard' positions again with 2000K nodes
(those not found by both engines in 200K nodes):

master: 1069
new:    1395

bench: 7710548
Simplify a condition in is_KXK()

No functional change.
Merge branch 'master' into passed_pawns