function checkUncheckAll(formobj, check) {
        for (var i = 0; i < formobj.elements.length; i++) {
                if (formobj.elements[i].type == "checkbox") {
                        formobj.elements[i].checked = check;
                }
        }
}

function swapChecked(formobj) {
        var some_unchecked = 0;

        for (var i = 0; i < formobj.elements.length; i++) {
                if ( formobj.elements[i].type == "checkbox" && ! formobj.elements[i].checked ) {
                        some_unchecked = 1;
                        break;
                }
        }

        if ( some_unchecked ) {
                checkUncheckAll(formobj,1);
        } else {
                checkUncheckAll(formobj,0);
        }
}