Throw an error when nothing will work.

exec/load/dns.js

@@ -280,6 +280,9 @@ function DNS(servers) {
 		this.sockets.push(sock);
 	}, this);
 
+	if (this.sockets.length < 1)
+		throw('Unable to create any sockets');
+
 	increment_id = function() {
 		var ret = nextid;
 		do {