Try hard not to lose on time

We try hard not to lose on time even under extreme
time pressure. We achieve this through 3 different but
coordinated steps:

    1) Increase max frequency of timer events

    2) Quickly return after a stop signal

    3) Take in account timer resolution

With these SF played under LittleBlitzer at 1"+0.02 and 3"+0
without losing on time even one game.

No functional change.

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

src/thread.cpp

@@ -367,7 +367,7 @@ template Value ThreadsManager::split<true>(Position&, Stack*, Value, Value, Valu
 
 // Thread::timer_loop() is where the timer thread waits maxPly milliseconds and
 // then calls do_timer_event(). If maxPly is 0 thread sleeps until is woken up.
-extern void do_timer_event();
+extern void check_time();
 
 void Thread::timer_loop() {
 
@@ -376,7 +376,7 @@ void Thread::timer_loop() {
       lock_grab(&sleepLock);
       timed_wait(&sleepCond, &sleepLock, maxPly ? maxPly : INT_MAX);
       lock_release(&sleepLock);
-      do_timer_event();
+      check_time();
   }
 }