Callback on an event

Property definitions

	# Callback on an event
	fun callback(events: Int) do end

lib/libevent/libevent.nit:146,2--147,33

	redef fun callback(events)
	do
		event_base.loopexit
		for handler in signal_handlers do handler.del
	end

lib/nitcorn/signal_handler.nit:34,2--38,4