Enable IID at non-PV nodes

We want to increrase the opportunities
of doing an exclusion search.

After 999 games at 1+0
Mod vs Orig +216 =574 -209 50.35%  503.0/999  +2 ELO

Signed-off-by: Marco Costalba <mcostalba@gmail.com>

src/search.cpp

@@ -139,7 +139,7 @@ namespace {
 
   // Use internal iterative deepening?
   const bool UseIIDAtPVNodes = true;
-  const bool UseIIDAtNonPVNodes = false;
+  const bool UseIIDAtNonPVNodes = true;
 
   // Internal iterative deepening margin. At Non-PV moves, when
   // UseIIDAtNonPVNodes is true, we do an internal iterative deepening