function check_login(captcha)
{
  m_alert = "";
  
	if(document.getElementById('login_username').value.replace(/^\s+|\s+$/g,'') == '')
    m_alert += "Please enter your username.\n";
    
  if(document.getElementById('login_password').value.replace(/^\s+|\s+$/g,'') == '')
    m_alert += "Please enter your password.\n";
    
  //if(captcha && document.getElementById('captcha').value.replace(/^\s+|\s+$/g,'') == '')
    //m_alert += "Please, type the characters you see in the picture.\n";
    
  return m_alert;
}