Variables:
	$apt_clean: Sets DSelect::Clean, defaults to 'auto' on normal hosts and
		'pre-auto' in vservers, since the latter are usually more space-bound and
		have better recovery mechanisms via the host
		From apt.conf(5), 0.7.2: "Cache Clean mode; this value may be one of
			always, prompt, auto, pre-auto and never. always and prompt will
			remove all packages from the cache after upgrading, prompt (the
			default) does so conditionally.  auto removes only those packages
			which are no longer downloadable (replaced with a new version for
			instance). pre-auto performs this action before downloading new
			packages."

Provided Resources:
	File[apt_config]: Use this resource to depend on or add to a completed apt
		configuration
	Exec[apt_updated]: After this point, current packages can installed via apt,
		usually used like this:
		Package { require => Exec[apt_updated] }