Pass a CGIURL into commentmoderation.tmpl

Omitting this resulted <form action=""> which is in fact a working
self-referential form, but is less obvious than it ought to be.

IkiWiki/Plugin/comments.pm

@@ -656,6 +656,7 @@ sub commentmoderation ($$) {
 	$template->param(
 		sid => $session->id,
 		comments => \@comments,
+		cgiurl => IkiWiki::cgiurl(),
 	);
 	IkiWiki::printheader($session);
 	my $out=$template->output;