make a more descriptive error message when CURLE_HTTP_RETURNED_ERROR is

                  /* If we have been told to fail hard on HTTP-errors,

                     here is the check for that: */

                  /* serious error, go home! */

                  failf (data, "The requested file was not found");

                  failf (data, "The requested URL returned error: %d",

                         k->httpcode);

                  return CURLE_HTTP_RETURNED_ERROR;

                }