don't link to index.php on sql-error but rather to the page before the error

Signed-off-by: Michael Kaufmann (d00p) <d00p@froxlor.org>
let the admin set the server-alias completely (either wildcard, www. or none), customer option follows, this fixes #1147

Signed-off-by: Michael Kaufmann (d00p) <d00p@froxlor.org>