[MERGE] Add InterBranch.update_references()

[Aaron Bentley]

Aaron Bentley has voted comment.
Status is now: Semi-approved
Comment:
Martin has announced a moratorium on Nested Trees reviews until we get 
the whole "what should the design be" issue sorted out.  So, not 
reviewing.

For details, see: 
http://bundlebuggy.aaronbentley.com/project/bzr/request/%3C20090506180919.GA30992%40vernstok.nl%3E
Project: Bazaar