[MERGE] add hook to inspect and modify url for fallback location of a branch

[John Arbash Meinel]

John Arbash Meinel has voted approve.
Status is now: Conditionally approved
Comment:
I think it is fine to declare the ordering undefined, and we can just do 
that in the documentation comment.


For details, see: 
http://bundlebuggy.aaronbentley.com/project/bzr/request/%3C48ED5C67.9020408%40canonical.com%3E
Project: Bazaar