Failed initial scans require manual cleanup

[William Grant]

If the initial scan of a branch commits branchrevisions then dies, we end up with a branch with revisions but last_scanned IS NULL. The next scan run will attempt to do an initial scan, try to insert the same branchrevisions, and die like this:

OOPS-1871SMS100
IntegrityError: duplicate key value violates unique constraint "revision__branch__revision__key"

Currently this needs manual DB cleanup with https://pastebin.canonical.com/43260/.

[William Grant (wgrant)]

BzrSync.getAncestryData assumes the absence of data if last_scanned_id is unset.

[Aaron Bentley (abentley)]

OOPS-1985SMS60 has the same traceback, but refers to an already-scanned branch. So I think this issue may not be limited only to initial scans.

[Launchpad QA Bot (lpqabot)]

Fixed in stable r13241 <http://bazaar.launchpad.net/~launchpad-pqm/launchpad/stable/revision/13241>.