Callback on listening error

Property definitions

libevent $ ConnectionListener :: error_callback
	# Callback on listening error
	fun error_callback
	do
		var cstr = evutil_socket_error_to_string(evutil_socket_error)
		print_error "libevent error: {cstr}"
	end
lib/libevent/libevent.nit:473,2--478,4