[MERGE] add a hook for Branch.set_last_revision_info()

[Andrew Bennetts]

Andrew Bennetts has voted approve.
Status is now: Approved
Comment:
I'll send this to PQM.

For details, see: 
http://bundlebuggy.aaronbentley.com/request/%3Ca7e835d40804090015i411697bp46698d4395ced7fd%40mail.gmail.com%3E