Make event-handlers edge-triggered and move socket-state to Dart.

tests/standalone/io/http_server_test.dart

 // Copyright (c) 2013, the Dart project authors.  Please see the AUTHORS file
 // for details. All rights reserved. Use of this source code is governed by a
 // BSD-style license that can be found in the LICENSE file.
 
 import "dart:async";
 import "dart:io";
 
 import "package:async_helper/async_helper.dart";
 import "package:expect/expect.dart";
 
@@ skipping 83 matching lines @@
         request.listen((_) {}, onError: (error) {
           Expect.notEquals(Zone.ROOT, Zone.current);
           server.close();
           throw error;
         });
       });
       Socket.connect("127.0.0.1", server.port).then((socket) {
         socket.write('GET / HTTP/1.1\r\nContent-Length: 100\r\n\r\n');
         socket.write('some body');
         socket.close();
+        socket.listen(null);
       });
     });
   }, onError: (e) {
     asyncEnd();
   });
 }
 
 
 void main() {
   testListenOn();
   testHttpServerZone();
   testHttpServerZoneError();
 }