[merge] make RevisionSpec_revid always return a str

[John Arbash Meinel]

John Arbash Meinel has voted +1 (conditional).
Status is now: Semi-approved
Comment:
No problem with %s => %r, these are just errors given to users for when 
things break.

The only thing I would add, is that RevisionSpec.from_string() should 
also be able to handle a non-unicode string.

So it would be nice to add

self.assertInHistory(3, rev_id, 'revid:'+rev_id)

I'm not going to be a stickler for it, because adding 'revid:' makes 
from_string() very much a user-facing api.

Otherwise +1 from me.

For details, see: 
http://bundlebuggy.aaronbentley.com/request/%3C20070308190232.GB3806%40cyclops.localdomain%3E