function startswith(str, start) {return (str.match('^'+start)==start);}

function marca_todos()
{
    var prefix = this.id;
    var qualform = document.getElementById("form-inscricao");
    for (var i=0; i<qualform.elements.length; i++) {
        var element = qualform.elements[i];
        if (element.type == "checkbox")
        {
            if (startswith(element.id,prefix))
                element.checked = true;
        }
    }
}

function def_click() {
  var qualform = document.getElementById("form-inscricao");
  for (var i=0; i<qualform.elements.length; i++) {
    var element = qualform.elements[i];
    if (element.type == "checkbox")
    {
        if (startswith(element.name,"todos"))
            element.onclick = marca_todos;
    }
  }
}

addLoadEvent(def_click);