[MERGE] Support multiple authors for a revision (#185772)

[Aaron Bentley]

Aaron Bentley has voted abstain.
Status is now: Semi-approved
Comment:
I don't think we should change the meaning of existing tags.  Why not 
introduce a new tag?  Old clients will ignore it, and new clients will 
work fine.

For details, see: 
http://bundlebuggy.aaronbentley.com/project/bzr/request/%3C1235677078.12856.4.camel%40flash%3E
Project: Bazaar