$(document).ready(function() {
    var navlist = $("ul.navigation-list");
    var images = $("img", navlist);

    images.each(function() {
        var t = $(this), src = t.attr("src"), fn = src.split(".");
        var isActive = src.indexOf("_hover") != -1 ? true : false;
        var hover = fn[0] + "_hover." + fn[1];

        t.hover(function() {
            if(!isActive) t.attr("src", hover);
        },
        function() {
            if(!isActive) t.attr("src", src);
        });
    });
});