Updated class to use "protected" instead of "private" access modifier.

I ran into an issue when extending the IronCache class. Since everything was private, it made the following impossible since I needed access to the private variable "cache_name". In general I think protected is a far better way of shielding access while being flexible enough to allow extendability.

    class FlexIronCache extends IronCache {
      public function put($key, $item){
        if (is_array($item) || is_object($item)) {
          $item = serialize($item);
        }
        return $this->putItem($this->cache_name, $key, $item);
      }
      public function get($key){
        $val = $this->getItem($this->cache_name, $key);
        $unserialised = @unserialize($val);
        return $unserialised !== FALSE ? $unserialised : $val;
      }
    }