fixed one-liners for file and directory

sdk/lib/io/file.dart

 // Copyright (c) 2013, 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;
 
 /**
  * FileMode describes the modes in which a file can be opened.
  */
 class FileMode {
   static const READ = const FileMode._internal(0);
   static const WRITE = const FileMode._internal(1);
   static const APPEND = const FileMode._internal(2);
   const FileMode._internal(int this._mode);
   final int _mode;
 }
 
 const READ = FileMode.READ;
 const WRITE = FileMode.WRITE;
 const APPEND = FileMode.APPEND;
 
 /**
- * [File] objects are references to files.
+ * A reference to a file on the file system.
  *
  * If [path] is a symbolic link, rather than a file, then
  * the methods of [File] operate on the ultimate target of the
  * link, except for File.delete and File.deleteSync, which operate on
  * the link.
  *
  * To operate on the underlying file data there are two options:
  *
  *  * Use streaming: read the contents of the file from the [Stream]
  *    this.[openRead]() and write to the file by writing to the [IOSink]
@@ skipping 500 matching lines @@
       }
     } else if (osError != null) {
       sb.write(": osError");
       if (path != null) {
         sb.write(", path = $path");
       }
     }
     return sb.toString();
   }
 }