fixup debian/munin-async.logrotate (Closes: #691758)

* debian/munin-async.logrotate:
  - use adm group for created files.
  - use *0 as glob, not *.0 (Closes: #691758)
release as 2.0.6-3 to sid
improve debian/*.postinst

* debian/*.postinst:
  - only (try to) create users on first install, not on every upgrade.
  - only configure apache on first install.
  - add better comments what legacy code to remove after
  squeeze-sloppy-backports.
release as 2.0.9-3 to Debian experimental