public function addVarnishHeader($name, $value)
    {
        $header = $value;
        
        if ($this->hasVarnishHeader($name)) {
            $header = $this->getVarnishHeader($name);
            
            if (!is_array($header)) {
                $header = array($header);
            }
            
            $header[] = $value;
        } 
        
        $this->setVarnishHeader($name, $header);
        
        return $this;
    }