http_server: prefinish vs finish

Do not detach the socket from the response until all data is actually
sent to the other side.

See: nodejs#1373

lib/_http_server.js

@@ -429,7 +429,7 @@ function connectionListener(socket) {
 
  // When we're finished writing the response, check if this is the last
  // respose, if so destroy the socket.
- res.on('prefinish', resOnFinish);
+ res.on('finish', resOnFinish);
  function resOnFinish() {
  // Usually the first incoming element should be our request. it may
  // be that in the case abortIncoming() was called that the incoming