CVE-2013-6401: Change hash function, randomize hashes

Thanks to Florian Weimer and Eric Sesterhenn for reporting, reviewing
and testing.
int json_real_set(json_t *json, double value)
{
    if(!json_is_real(json) || isnan(value) || isinf(value))
        return -1;

    json_to_real(json)->value = value;

    return 0;
}

int json_real_set(json_t *json, double value)
{
    if(!json_is_real(json) || isnan(value) || isinf(value))
        return -1;

    json_to_real(json)->value = value;

    return 0;
}
