Split dart:builtin into dart:builtin and dart:io.

samples/markdown/markdown.dart

-// Copyright (c) 2011, the Dart project authors.  Please see the AUTHORS file
+// 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.
 
 /// Standalone script for parsing markdown from files and converting to HTML.
 #library('markdown_app');
 
+#import('dart:io');
 #import('lib.dart');
 
 main() {
   final args = (new Options()).arguments;
 
   if (args.length > 2) {
     print('Usage:');
     print('  dart markdown.dart <inputfile> [<outputfile>]');
     print('');
     print('Reads a file containing markdown and converts it to HTML.');
@@ skipping 19 matching lines @@
   file.closeSync();
   return new String.fromCharCodes(buffer);
 }
 
 void writeFile(String path, String text) {
   final file = new File(path);
   final stream = file.openOutputStream();
   stream.write(text.charCodes());
   stream.close();
 }