* Sync systemd units with upstream. Upstream uses SIGUSR2 instead of SIGHUP
to reload the clamd service.
* Convert freshclam service to a oneshot service activated by a systemd timer.
This way we can make clamd wait for freshclam to finish fetching the virus
database before failing to start if the database doesn't exist yet.
* Fixes console tools to work as expected as they require hardcoded config
file locations.
- Add new service for `clamd`, the ClamAV daemon.
- Replace the old upstart "jobs" section with systemd.services
- Remove unnecessary config options.
- Use `mkEnableOption`
Using pkgs.lib on the spine of module evaluation is problematic
because the pkgs argument depends on the result of module
evaluation. To prevent an infinite recursion, pkgs and some of the
modules are evaluated twice, which is inefficient. Using ‘with lib’
prevents this problem.
