Using packages currently built as deps for another build

[Bruno Cornec]

When building the project project-builder and invoking make test, we need another akcage which is perl-ProjectBuilder. However, as we are building packages in that one may not be there yet (of course we are using the previous version most of the time, but that's not what you want). So we should be able to provide an order for building packages, and layers of build based on which package needs which.