Code review comment for ~nacc/git-ubuntu:lp1730734-cache-importer-progress

> Aother thought, does the cache need to be distinct for debian/ubuntu X
> unapplied/applied? Given that applied failures may be fixable, they can be at
> a different version than the unapplied?

I do think we actually need 4 caches, since the unapplied / applied heads can easily be at a different state. I'll work on this now.

I'll also add some changes to the importer to clean up that code.