Fix the directory index test

Related to #104
I see.
I guess (theoretically at least) if you had a really deep file-path like `some/crazy/long/deeply/nested/path/to/myfile.html` and you accidentally linked to `some/crazy/long/deply/nested/path/to/myfile.html`, it might be nice to know which part of the directory-tree the first error occurred in? ;)
(but obviously you could only do that for local paths, it wouldn't generally work for external links)

Apologies if I'm sending things OffTopic!