Set default action for the signal

Property definitions

signals $ SignalHandler :: default_signal
	# Set default action for the signal
	fun default_signal(signal: Int) `{
		if (signal < 32 && signal >=0) {
			struct sigaction act;
			sigemptyset(&act.sa_mask);
			act.sa_flags = 0;
			act.sa_handler = SIG_DFL;
			sigaction(signal, &act, NULL);

		#ifdef SignalHandler_decr_ref
			SignalHandler last_handler = (SignalHandler)nit_signals_list[signal].handler;
			if (last_handler != NULL)
				SignalHandler_decr_ref(last_handler);
		#endif
		}
	`}
lib/signals/signals.nit:189,2--204,3