Move MimeMultipartTransformer and HttpBodyHandler to mime and http_server packages.

pkg/http_server/lib/src/http_multipart_form_data_impl.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.
 
-part of dart.io;
+part of http_server;
 
 
 class _HttpMultipartFormData extends Stream implements HttpMultipartFormData {
   final ContentType contentType;
   final HeaderValue contentDisposition;
   final HeaderValue contentTransferEncoding;
 
   final MimeMultipart _mimeMultipart;
 
   bool _isText = false;
@@ skipping 113 matching lines @@
     while ((amp = input.indexOf('&', offset)) >= 0) {
       buffer.write(input.substring(offset, amp));
       int end = input.indexOf(';', amp);
       parse(amp, end);
       offset = end + 1;
     }
     buffer.write(input.substring(offset));
     return buffer.toString();
   }
 }
-