Use a semicolon as the separator for multipart form-data requests.

pkg/http/lib/src/multipart_request.dart

 // Copyright (c) 2012, 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.
 
 library multipart_request;
 
 import 'dart:io';
 import 'dart:math';
 import 'dart:uri';
 import 'dart:utf';
@@ skipping 63 matching lines @@
   MultipartRequest(String method, Uri url)
     : super(method, url),
       fields = <String>{},
       files = <MultipartFile>[];
 
   /// Freezes all mutable fields and returns an [InputStream] that will emit the
   /// request body.
   InputStream finalize() {
     // TODO(nweiz): freeze fields and files
     var boundary = _boundaryString(_BOUNDARY_LENGTH);
-    headers['content-type'] = 'multipart/form-data, boundary="$boundary"';
+    headers['content-type'] = 'multipart/form-data; boundary="$boundary"';
     headers['content-transfer-encoding'] = 'binary';
     super.finalize();
 
     var stream = new ListInputStream();
 
     void writeAscii(String string) {
       assert(isPlainAscii(string));
       stream.write(string.charCodes);
     }
 
@@ skipping 62 matching lines @@
   String _boundaryString(int length) {
     var prefix = "dart-http-boundary-";
     var list = new List<int>(length - prefix.length);
     for (var i = 0; i < list.length; i++) {
       list[i] = _BOUNDARY_CHARACTERS[
           _random.nextInt(_BOUNDARY_CHARACTERS.length)];
     }
     return "$prefix${new String.fromCharCodes(list)}";
   }
 }