/*! Updates the selected navigation tab */
function selectTab(tabId) {
    var nav = document.getElementById("main_navigation");
    var items = nav.getElementsByTagName("li");
    var i = 0;
    for (; i < items.length; ++i) {
        var item = items[i];
        if (item.id == tabId) {
            item.className="current";
        } else {
            item.className="normal";
        }
    }   
}