[MERGE] Define error for Repository.revision_tree()

[John Arbash Meinel]

John Arbash Meinel has voted -1.
Status is now: Vetoed
Comment:
I've taken far to long to clean this up, so I'm abandoning it for now.

The branch is available at:
https://code.launchpad.net/~jameinel/bzr/revision-tree-errors

if someone else wants to pick it up.

For details, see: 
http://bundlebuggy.aaronbentley.com/request/%3C45D6718A.5060801%40arbash-meinel.com%3E