currently source packages which only have arch-all-packages are not in
the wanna-build database. This however might have an interessting
effect if a package becomes an arch-all-package.
I see three ways handling that:
1. Put all arch-all-only-packages into the database
2. Remove a package when it becomes arch-all-only from the database
3. Keep packages in the database if they're historically there, but
don't add fresh arch-all-only-packages there
What do you think? (The last one is ugly, the second one might loose
old failed log entries)