[merge] [#252428] allow upgrade of stacked branches

[Bundle Buggy]

Bundle Buggy has detected this merge request.

For details, see: 
http://bundlebuggy.aaronbentley.com/project/bzr/request/%3Ce01316480808040016h4deae0daxa9e4a981983d7206%40mail.gmail.com%3E
Project: Bazaar