Compatibility with Postfix 3

[runejuhl]

Postfix 3 introduces a compatibility_level setting and changes the default value of daemon_directory.

Also includes linting of primarily trailing spaces.

[eLvErDe]

Hi,

Would you consider adding Raspbian (Debian built for RaspberryPi in this pull request).

In params.pp

        'Debian', 'Raspbian': {
          $daemon_directory = $::lsbdistcodename ? {
            /(wheezy|jessie)/ => '/usr/lib/postfix',
            default           => '/usr/lib/postfix/sbin',
          }
        }

[lvicainne]

Hello ! @thias , it could be a nice thing to merge this PR ! :-) Thanks !