Fix: Unsupported method in request may show raw binary data in log.

Fix: Unsupported method in request may show raw binary data in log.

hp->buf which should be a plain text HTTP request is occasionally full of
binary garbage.

 * replace any non-printables with underscores.

 * crop the output at 100 chars, we should not need a whole binary
   streaming video to identify the issue.

 * reference extension_methods for admin if its a genuine request.