[MERGE] fix handling of stacked-on branch in smart server

[Jonathan Lange]

Jonathan Lange has voted tweak.
Status is now: Conditionally approved
Comment:
Looks good to me.

Tests without assertions weird me out. It'd be nice if you could add a 
comment saying why one's not necessary.

For details, see: 
http://bundlebuggy.aaronbentley.com/project/bzr/request/%3C491A1522.2000806%40aaronbentley.com%3E
Project: Bazaar