Implement toString on File and Directory objects.

tests/standalone/io/directory_test.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.
 //
 // Directory listing test.
 
 import "dart:io";
 import "dart:isolate";
 
 class DirectoryTest {
   static void testListing() {
     bool listedDir = false;
     bool listedFile = false;
 
     Directory directory = new Directory("").createTempSync();
     Directory subDirectory = new Directory("${directory.path}/subdir");
+    Expect.isTrue('$directory'.contains(directory.path));
     Expect.isFalse(subDirectory.existsSync());
     subDirectory.createSync();
     Expect.isTrue(subDirectory.existsSync());
     File f = new File('${subDirectory.path}/file.txt');
     Expect.isFalse(f.existsSync());
     f.createSync();
 
     var lister = directory.list(recursive: true);
 
     lister.onDir = (dir) {
@@ skipping 561 matching lines @@
   testCreateTempErrorSync();
   testCreateTempError();
   testCreateExistingSync();
   testCreateExisting();
   testCreateDirExistingFileSync();
   testCreateDirExistingFile();
   testCreateRecursive();
   testCreateRecursiveSync();
   testRename();
 }