Make git rebase-update more responsive.

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 46 matching lines @@
     # TODO(iannucci): assert that the tags are in the remote fetch refspec
     fetch_args = ['--all']
   else:
     fetch_args.append('--multiple')
     fetch_args.extend(remotes)
   # TODO(iannucci): Should we fetch git-svn?
 
   if not fetch_args:  # pragma: no cover
     print 'Nothing to fetch.'
   else:
-    out, err = git.run_with_stderr('fetch', *fetch_args)
-    for data, stream in zip((out, err), (sys.stdout, sys.stderr)):
-      if data:
-        print >> stream, data
+    git.run_with_stderr('fetch', *fetch_args, stdout=sys.stdout,
+                        stderr=sys.stderr)
 
 
 def remove_empty_branches(branch_tree):
   tag_set = git.tags()
   ensure_root_checkout = git.once(lambda: git.run('checkout', git.root()))
 
   deletions = set()
   downstreams = collections.defaultdict(list)
   for branch, parent in git.topo_iter(branch_tree, top_down=False):
     downstreams[parent].append(branch)
@@ skipping 163 matching lines @@
           % (return_branch, root_branch)
         )
       git.run('checkout', root_branch)
     git.set_config(STARTING_BRANCH_KEY, '')
 
   return retcode
 
 
 if __name__ == '__main__':  # pragma: no cover
   sys.exit(main(sys.argv[1:]))