http_server: `prefinish` vs `finish`

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

See: https://github.com/iojs/io.js/pull/1373
PR-URL: https://github.com/nodejs/io.js/pull/1411
Reviewed-By: Chris Dickinson <christopher.s.dickinson@gmail.com>
Reviewed-By: Jeremiah Senkpiel <fishrock123@rocketmail.com>

lib/_http_server.js

@@ -431,7 +431,7 @@ 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