Do lmr for more captures

Based on machinery introduced by vondele. Logic behind patch if relatively simple -
if we reduce less with high hit rate of transposition table somewhat logical is to
reduce more with low hit rate. For example enable all captures for LMR.

Threshold 0.375 is arbitrary and can be tweaked :)

STC
http://tests.stockfishchess.org/tests/view/5dd4d51df531e81cf278eaac
LLR: 2.97 (-2.94,2.94) [-1.50,4.50]
Total: 16495 W: 3591 L: 3434 D: 9470

LTC
http://tests.stockfishchess.org/tests/view/5dd52265f531e81cf278eace
LLR: 2.96 (-2.94,2.94) [0.00,3.50]
Total: 23598 W: 3956 L: 3716 D: 15926

Closes #2420

Bench: 5067870

src/search.cpp

@@ -1084,7 +1084,8 @@ namespace {
           && (  !captureOrPromotion
               || moveCountPruning
               || ss->staticEval + PieceValue[EG][pos.captured_piece()] <= alpha
-              || cutNode))
+              || cutNode
+              || thisThread->ttHitAverage < 384 * ttHitAverageResolution * ttHitAverageWindow / 1024))
       {
           Depth r = reduction(improving, depth, moveCount);