message: Better usage of std::chrono
diff: @@ -110,7 +110,7 @@ public:
  {
  using clock = std::chrono::system_clock;
  const auto deadline =
  - tp ? clock::time_point(std::chrono::seconds(tp->tv_sec) + std::chrono::nanoseconds(tp->tv_nsec))
  + tp ? clock::time_point::ceil(clock::from_time_t(tp->tv_sec) + std::chrono::nanoseconds(tp->tv_nsec))
  : clock::time_point();
  while (!cond()) {
  wait(m, tp);
  