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

[Martin Pool]

It turns out this is pretty trivially fixed...

It might be better to remove, or move, this section altogether, but
I'll leave that unless someone else has a clear opinion.

I'm also going to change this test into a scenario test run for
various interesting format combinations and see what happens.

-- 
Martin <http://launchpad.net/~mbp/>
-------------- next part --------------
A non-text attachment was scrubbed...
Name: 20080804-252428-stacked-upgrade.diff
Type: text/x-diff
Size: 6255 bytes
Desc: not available
Url : https://lists.ubuntu.com/archives/bazaar/attachments/20080804/b3369dce/attachment-0001.bin