Fixed: FS#2378 - $conf['theme'] value in interface/lib/config.inc.php is overwritten (reset to 'default') on update

Implemented: FS#2283 - Add O option to dovecot transport in postfix master.cf so that X-Original-To: header is added.

- install: touch auth.log
- login: write success/fail to auth.log
- cron: log rotation for auth.log

Merged revisions 3049-3051,3053-3054,3058,3070,3074-3077,3082,3086-3088,3091-3092,3094-3095 from stable branch.

- Make sure the apps vhost gets configured no matter if the ISPConfig interface is installed or not.

replaced "listen ... ssl;" through "ssl on;" in nginx (ispconfig.vhost) in case that ssl is used for ispconfig

Fixed: PHP Fatal error:  Cannot use string offset as an array in /tmp/trunk/install/lib/installer_base.lib.php on line 638

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- Installer adds Apache and nginx user to ispapps group.
- Installer makes sure that /var/www/apps has 755 permissions.

- Added empty function configure_fail2ban() to get rid of the following fatal error during installation on non-Debian/Ubuntu systems: PHP Fatal error:  Call to undefined method installer::configure_fail2ban() in /tmp/trunk/install/install.php on line 266

- Fixed "PHP Notice:  Undefined property: installer::$ispconfig_interface_installed in /tmp/trunk/install/update.php on line 337" when updating an ISPConfig server with nginx.