Report 404 as an error on the source page instead of destination

[mthuurne]

When a resource is not found (HTTP status 404), this is reported as an error on a non-existing page. Typically these problems are caused by broken links though, which are located on the referring page. So the report would be easier for the user to process if 404's are included in the referrer's section.

[mthuurne]

Maybe the same applies to other client error (4xx) status codes: if the server thinks the client is wrong in asking these, then the problem should be reported on the page(s) that generated the request.

Perhaps we don't need the "referenced by" section of the page report anymore once we report client errors on the referrer. The reason I originally added it was to find out where the links came from in case the link itself was broken.

[mthuurne]

I went through all 4xx status codes and found the following that should be reported on the source page:

• 400 Bad Request
• 404 Not Found
• 405 Method Not Allowed
• 410 Gone
• 414 URI Too Long