iterating over revisions in a branch

[Jamie Wilkinson]

This one time, at band camp, Robert Collins wrote:
>There was some serious concerns about efficiency some time back, and we
>had two concepts - revision_id and revision - floating around, with
>inconsistent apis here and there. I'd like us to have lazy constructed
>revisions that would take the place of revisionids in all apis *except
>those used to instantiate revisions or translate from the UI* (i.e.
>has_revision, get_revision & RevisionSpecs).  IIRC John and Aaron had
>concerns that this would mask problems where a revision was not present
>in the store, and some code wanted to check that it was present.
>
>I thought that that was best checked by
>'repository.has_revision(revision.id)' 
>
>Anyway, thats how we got where we are, I'd love to see this cleaned up
>some way or another, just need consensus on whats the right mental
>model.

Ok, so I just got here in the middle of it :)

>Mine is 'the library apis in general deal with revisions, not revision
>ids'

Cool :)