Fixed (partly) FS#2310 - Template switch not working in mailuser module, for dashlets and the login page

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

- Added PHP-FPM pm settings (pm.max_children, pm.start_servers, pm.min_spare_servers, pm.max_spare_servers) to the "Options" tab of a website.

- 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.

Implemented: FS#1113 - Force client to use only allowed IPs

- Added SEO redirects (both Apache & nginx) to redirect from non-www website to www website or vice versa.
- Introduced placeholder [scheme] for redirect paths for alias and subdomains; will be replaced with http or https, depending on what the visitor uses.

Fixed: PHP notice in tform_actions.inc.php

Removed unsupported setting in vhost config file and added german translation of welcome email message.

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Replaced old variable names with new ones used in apache 2, see here for reference: http://httpd.apache.org/mod_fcgid/mod/mod_fcgid.html

Temporary fix for: FS#1311 - Only first PHPINIDir directive honored per configuration tree - subsequent ones ignored 

- Fixed a formatting problem with suphp.conf and newer suphp versions.

Merged revisions 1832-1836 from stable (added dovecot support for debian squeeze and added a new distid and class for debian6 specific modifications.