Implement automatic loading of dart:core_native_fields library

bin/builtin.dart

 // Copyright (c) 2011, 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("builtin");
+#import("dart:nativewrappers");
+#import("dart:coreimpl");
 
 void print(arg) {
   _Logger._printString(arg.toString());
 }
 
 void exit(int status) {
   if (status is !int) {
     throw new IllegalArgumentException("int status expected");
   }
   _exit(status);
@@ skipping 26 matching lines @@
   return _stderr.outputStream;
 }
 
 _exit(int status) native "Exit";
 
 _getStdioHandle(Socket socket, int num) native "Socket_GetStdioHandle";
 
 class _Logger {
   static void _printString(String s) native "Logger_PrintString";
 }