Override lintian error: service-file-is-not-a-file

The "munin" unit needs to be masked, since its function is handled by
tmpfiles.d when using systemd.

From the systemd manual:

  If a unit file is empty (i.e. has the file size 0) or is symlinked to
  /dev/null its configuration will not be loaded and it appears with a load
  state of "masked", and cannot be activated. Use this as an effective way to
  fully disable a unit, making it impossible to start it even manually.
Ensure munin.init calls /lib/lsb/init-functions
Really remove the link in /etc/apache2/conf-available/

Beforehand we checked if the file exists but the link is already broken so
nothing was removed.
Fix munin configuration for apache2.4

* The apache2-maintscript-helper doesn't work if called from a function (what
  we do) so we give $@ of the postinst to the apache_install function.

* Don't remove the configuration from apache 2.4 on removal of munin. This is
  the same behavior as we do it with apache 2.2.
Document previous commits in changelog
Fix minor wording
Add the missing part to the apache2.4 / apache2.2 fixes

* If conf.d/ still exists apache would restarted before the broken munin.conf
  link from conf-available/ could be removed. Making the apache restart after
  the removal from conf.d/ conditional fixes this issue.
Merge branch 'debian' of ssh://git.debian.org/git/collab-maint/munin into debian

fixed Conflicts:
	debian/changelog