* Do HTTP head request first when loading database from mirror to avoid
downloading the full database all the time
* Use the last modification date of the local database file because with
the persistent storage even local database reloads became a bit expensive
Simply adding `--sign` to the `makepkg` flags doesn't work because it would
require setting up GPG within the chroot environment (of `makechrootpkg`).
When debugging it is anyways annoying that `makepkg` sends the `gpg` output
to `/dev/null`. This way the logs are preserved.