this also fixes a problem with ignored vhost subdomains on validation

Fixed: reseller has_clients if limit_client is != 0, e.g. -1 or > 0. Thanks to Sergio for pointing out this issue.

- Make sure ISPConfig shows the correct error message (instad of an SQL error) when a website is renamed after an alias domain that still exists.
- It should be possible to create two websites with the same domain on the same server as long as the IP differs. I therefore changed the serverdomain index of the web_domain table to include the IP address.

- Added missing option in centos dovecot.conf file

- Updated version number to 3.0.5.4rc1

- Added function to detect the apache version to installer.
- Added support for apache 2.4 to vhots templates for ispconfig vhost and apps vhost in installer.

This reverts commit 4cd62d78.