Option to check non-OK document bodies as well

[mthuurne]

Currently APE will only check a document body if the HTTP status code was 200 (OK). For other status codes, it will log a message like "Skipping content check because of HTTP status 404".

The reason for this behavior is that a lot of web servers have error and redirection notices that use archaic HTML. Running those through the checker would produce a lot of false positives.

However, if a web site or app uses custom error and redirection messages, it would be useful to check those. To make that possible, there would have to be a configuration option (off by default) to check the body for non-200 responses too. I don't know yet if it should be configurable per status code or just one flag for all non-200 codes.