Fix deprecation warnings in dart:io. Now completely warning free.

sdk/lib/io/http_impl.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.
 
 part of dart.io;
 
 class _HttpIncoming extends Stream<List<int>> {
   final int _transferLength;
   final Completer _dataCompleter = new Completer();
   Stream<List<int>> _stream;
@@ skipping 659 matching lines @@
       addString(uri.toString());
     }
     writeSP();
     add(_Const.HTTP11);
     writeCRLF();
 
     // Add the cookies to the headers.
     if (!cookies.isEmpty) {
       StringBuffer sb = new StringBuffer();
       for (int i = 0; i < cookies.length; i++) {
-        if (i > 0) sb.add("; ");
-        sb.add(cookies[i].name);
-        sb.add("=");
-        sb.add(cookies[i].value);
+        if (i > 0) sb.write("; ");
+        sb.write(cookies[i].name);
+        sb.write("=");
+        sb.write(cookies[i].value);
       }
       headers.add(HttpHeaders.COOKIE, sb.toString());
     }
 
     headers._finalize();
 
     // Write headers.
     headers._write(this);
     writeCRLF();
   }
@@ skipping 945 matching lines @@
 
 
 class _RedirectInfo implements RedirectInfo {
   const _RedirectInfo(int this.statusCode,
                       String this.method,
                       Uri this.location);
   final int statusCode;
   final String method;
   final Uri location;
 }