Fix multi-rename empty branch detection.

git_rebase_update.py

 #!/usr/bin/env python
 # Copyright 2014 The Chromium Authors. All rights reserved.
 # Use of this source code is governed by a BSD-style license that can be
 # found in the LICENSE file.
 
 """
 Tool to update all branches to have the latest changes from their upstreams.
 """
 
 import argparse
@@ skipping 75 matching lines @@
 def remove_empty_branches(branch_tree):
   tag_set = git.tags()
   ensure_root_checkout = git.once(lambda: git.run('checkout', git.root()))
 
   deletions = {}
   reparents = {}
   downstreams = collections.defaultdict(list)
   for branch, parent in git.topo_iter(branch_tree, top_down=False):
     downstreams[parent].append(branch)
 
-    # If branch and parent have the same state, then branch has to be marked
+    # If branch and parent have the same tree, then branch has to be marked
     # for deletion and its children and grand-children reparented to parent.
-    if git.hash_one(branch) == git.hash_one(parent):
+    if git.hash_one(branch+":") == git.hash_one(parent+":"):
       ensure_root_checkout()
 
       logging.debug('branch %s merged to %s', branch, parent)
 
       # Mark branch for deletion while remembering the ordering, then add all
       # its children as grand-children of its parent and record reparenting
       # information if necessary.
       deletions[branch] = len(deletions)
 
       for down in downstreams[branch]:
@@ skipping 210 matching lines @@
 
   return retcode
 
 
 if __name__ == '__main__':  # pragma: no cover
   try:
     sys.exit(main())
   except KeyboardInterrupt:
     sys.stderr.write('interrupted\n')
     sys.exit(1)