Generic fix for PR#31759

If a handler returns a value that is neither reserved nor a valid
HTTP response code, log an error and substitute HTTP_INTERNAL_SERVER_ERROR.
Allow a handler to override this explicitly by setting a note.


git-svn-id: https://svn.apache.org/repos/asf/httpd/httpd/trunk@448711 13f79535-47bb-0310-9956-ffa450edef68