Description of problem:
When using http://127.0.0.1:631/ to use the CUPS web API, the address is not seen as a loopback address and so the request is denied.

Version-Release number of selected component (if applicable):
cups-1.5.0-13.fc16.x86_64

Additional info:
It comes from this check:

int                                     /* O - 1 if local host, 0 otherwise */
httpAddrLocalhost(
    const http_addr_t *addr)            /* I - Address to check */
{
  if (!addr)
    return (1);

#ifdef AF_INET6
  if (addr->addr.sa_family == AF_INET6 &&
      IN6_IS_ADDR_LOOPBACK(&(addr->ipv6.sin6_addr)))
    return (1);
#endif /* AF_INET6 */

#ifdef AF_LOCAL
  if (addr->addr.sa_family == AF_LOCAL)
    return (1);
#endif /* AF_LOCAL */

  if (addr->addr.sa_family == AF_INET &&
      (ntohl(addr->ipv4.sin_addr.s_addr) & 0xff000000) == 0x7f000000)
    return (1);

  return (0);
}