Handle broken symlinks when creating package dirs.

utils/pub/entrypoint.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.
 
 library entrypoint;
 
 import 'dart:async';
 
 import '../../pkg/pathos/lib/path.dart' as path;
 
@@ skipping 273 matching lines @@
           return _listDirWithoutPackages(file);
         }).then((subfiles) {
           var fileAndSubfiles = [file];
           fileAndSubfiles.addAll(subfiles);
           return fileAndSubfiles;
         });
       }).toList());
     }).then(flatten);
   }
 
-  /// Creates a symlink to the `packages` directory in [dir] if none exists.
+  /// Creates a symlink to the `packages` directory in [dir]. Will replace one
+  /// if already there.
   Future _linkSecondaryPackageDir(String dir) {
     return defer(() {
       var symlink = path.join(dir, 'packages');
-      if (entryExists(symlink)) return;
-      return createSymlink(packagesDir, symlink, relative: true);
+      return new Future.of(() {
+        if (fileExists(symlink)) {
+          deleteFile(symlink);
+        } else if (dirExists(symlink)) {
+          return deleteDir(symlink);
+        }
+      }).then((_) => createSymlink(packagesDir, symlink, relative: true));
     });
   }
 }