Improve HTTP error message

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;
 
 const int _OUTGOING_BUFFER_SIZE = 8 * 1024;
 
 class _HttpIncoming extends Stream<List<int>> {
   final int _transferLength;
@@ skipping 1262 matching lines @@
 
     // Set up handlers on the parser here, so we are sure to get 'onDone' from
     // the parser.
     _subscription = _httpParser.listen(
         (incoming) {
           // Only handle one incoming response at the time. Keep the
           // stream paused until the response have been processed.
           _subscription.pause();
           // We assume the response is not here, until we have send the request.
           if (_nextResponseCompleter == null) {
-            throw new HttpException("Unexpected response.", uri: _currentUri);
+            throw new HttpException(
+                "Unexpected response (unsolicited response without request).",
+                uri: _currentUri);
           }
           _nextResponseCompleter.complete(incoming);
           _nextResponseCompleter = null;
         },
         onError: (error, [StackTrace stackTrace]) {
           if (_nextResponseCompleter != null) {
             _nextResponseCompleter.completeError(
                 new HttpException(error.message, uri: _currentUri),
                 stackTrace);
             _nextResponseCompleter = null;
@@ skipping 1507 matching lines @@
   const _RedirectInfo(this.statusCode, this.method, this.location);
 }
 
 String _getHttpVersion() {
   var version = Platform.version;
   // Only include major and minor version numbers.
   int index = version.indexOf('.', version.indexOf('.') + 1);
   version = version.substring(0, index);
   return 'Dart/$version (dart:io)';
 }