[merge] make RevisionSpec_revid always return a str

[John Arbash Meinel]

John Arbash Meinel has voted +1.
Status is now: Approved
Comment:
Yeah, I just wanted to mention it, to make sure other people knew about 
it. And give them an opportunity to discuss if they want to do it a 
different way.

I'll merge this.

For details, see: 
http://bundlebuggy.aaronbentley.com/request/%3C20070311181834.GA4419%40cyclops.localdomain%3E