Code review comment for lp:~maxb/udd/fix-import-ordering

@ james_w:

> Importing all Debian before any Ubuntu would prevent recording merges
> if Debian were to merge from Ubuntu. It's a rare case, so ok to sacrifice
> if this is needed to make other things work, but if we can preserve
> it it would be good.

That particular element of the ordering is pre-existing before my changes (though this branch adds the comment explaining it). I don't think it will be possible to remove it without significantly rewriting the ordering algorithm to either be based on a topological sort involving introspection of each version's debian/changelog, or to be a simple sort on the timestamp of the publishing records fetched from Launchpad.