Improve the caching when packages change in the repositories #2
Description
Right now, modian keeps a snapshot of the generated system at two times: after debootstrapping and after the full chroot has been generated; there is however no check of the package versions in the snapshots.
This works fine to improve the build times during quick development cycles, but it is important to remember that these caches are not safe to keep long term.
It would be nice if these caches were automatically invalidated when the versions of the installed packages is different from the one in the repository instead.