Enhancement: AFN: block duplicate forge URLs that differ only in presence/absence of trailing slash after domain name

AFNR#812 and AFNR#880 were allowed to be filed, despite the submitted URLs differing only in the presence/absence of the trailing slash / after the domain name.

Please block requests like this that differ only in presence/absence of the trailing slash after the domain name.

See also #4792 about stripping common URL suffixes when doing duplicate detection.