Make listenFD just DTRT after warning

lib/net.js

@@ -1072,8 +1072,13 @@ Server.prototype._emitCloseIfDrained = function() {
 };
 
 
+var listenFDwarn = false;
 Server.prototype.listenFD = function(fd, type) {
-  throw new Error('This API is no longer supported. See child_process.fork');
+  if (!listenFDwarn) {
+    console.error('listenFD is deprecated. Use server.listen()');
+    listenFDwarn = true;
+  }
+  this.listen({ fd: fd });
 };
 
 // when sending a socket using fork IPC this function is executed