Use a timer to avoid polling

The timer will be fired asynchronously to handle
time management flags, while other threads are
searching.

This implementation uses a thread waiting on a
timed condition variable instead of real timers.
This approach allow to reduce platform dependant
code to a minimum and also is the most portable given
that timers libraries are very different among platforms
and also the best ones are not compatible with olds
Windows.

Also retire the now unused polling code.

No functional change.

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

src/misc.h

@@ -22,12 +22,15 @@
 
 #include <fstream>
 #include <string>
+
+#include "lock.h"
 #include "types.h"
 
 extern const std::string engine_name();
 extern const std::string engine_authors();
 extern int get_system_time();
 extern int cpu_count();
+extern void timed_wait(WaitCondition*, Lock*, int);
 extern void prefetch(char* addr);
 
 extern void dbg_hit_on(bool b);