Fix for Directory.exists on Windows using GetFileAttributes

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 {
@@ skipping 233 matching lines @@
               });
             });
           });
         });
       });
     });
   }
 
   static void testExistsCreateDeleteSync() {
     Directory d = new Directory("").createTempSync();
+    Directory d2 = new Directory('${d.path}/');
     Expect.isTrue(d.existsSync());
+    Expect.isTrue(d2.existsSync());
     Directory created = new Directory("${d.path}/subdir");
     created.createSync();
     Expect.isTrue(created.existsSync());
     created.deleteSync();
     Expect.isFalse(created.existsSync());
     d.deleteSync();
     Expect.isFalse(d.existsSync());
   }
 
   static void testCreateTemp() {
@@ skipping 211 matching lines @@
   });
 }
 
 main() {
   DirectoryTest.testMain();
   NestedTempDirectoryTest.testMain();
   testCreateTempErrorSync();
   testCreateTempError();
   testRename();
 }