function sitenav(){
    var x=this;
    var p=document.getElementById("site-nav");
    var anchs=p.getElementsByTagName("a");
    x.active=null;
    
    this.init=function(){
        for(i=0;i<anchs.length;i++){

            anchs[i].onmouseover=function(){
                x.toggleOn(this);         
            }
            anchs[i].onmouseout=function(){
               x.toggleOff(this);
            }
        }
    }
    x.toggleOn=function(anch){
        if(anch.className!='active'){
        var img = anch.getElementsByTagName("img")[0];
        img.src=img.src.replace(".gif","_1.gif");
        }
    }
    
    x.toggleOff=function(anch){
        if(anch.className!='active'){
            var img = anch.getElementsByTagName("img")[0];
            img.src=img.src.replace("_1.gif",".gif");
        }
    }
    
    
    x.init();
}

window.onload=function(){
    var sn = new sitenav();   
}