Switched sync.{cpp,h} to std threading primitives.

src/util.h

@@ -28,6 +28,7 @@
 #include <vector>
 
 #include <boost/signals2/signal.hpp>
+#include <boost/thread/condition_variable.hpp> // for boost::thread_interrupted
 
 // Application startup time (used for uptime calculation)
 int64_t GetStartupTime();