branch-distro falls over on branch that didn't scan properly last time

[Michael Hudson-Doyle]

The branch-distro script fell over like this (https://pastebin.canonical.com/38573/) when it encountered this branch:

   https://code.launchpad.net/~ubuntu-branches/ubuntu/maverick/polybori/maverick

which didn't scan properly when maverick was opened. There are 17 branches that failed like this (https://pastebin.canonical.com/38575/) and it will fall over once for each of them.

The script needs to be more robust about such branches.

Also, we should figure out what's busted about these branches...

[Robert Collins (lifeless)]

This would/should have oopsed; clearly falls under that policy :)

[Curtis Hovey (sinzui)]

I believe we can unscan the each branch now. The fix for this might be for branch-distro's makeOneNewBranch() to call UnscanBranchScript when tip_revision is None, and carry on. When the main queue of branches is completed, it then processes the list unscanned branches. There is a timing issue where the unscan may not have been complete.

[Colin Watson (cjwatson)]

I removed branch-distro in r18583 due to disuse, so we won't be fixing this.