Replace fastcgi_pass unix:/var/run/php5-fpm.sock; with fastcgi_pass unix:{fpm_socket}; in phpmyadmin and squirrelmail blocks, as they are considered apps and should use the same (apps.sock) listener.

- Added check for the apps vhost to find out if the default PHP-FPM pool uses port 9000 or the socket /var/run/php5-fpm.sock.

- Changed FastCGI buffers for ISPConfig nginx vhost because otherwise you get "upstream sent too big header while reading response header from upstream" on OpenSUSE.
- Added 502 error page ("Bad Gateway").
- Added "fastcgi_intercept_errors on;" to nginx vhost template so that ISPConfig's error pages are displayed instead of the default nginx ones.