function popup(url) {
	var top=(screen.height-500)/2;
	var left=(screen.width-500)/2;
	window.open(url,"ajout_lien","top="+top+",left="+left+",width=500,height=520,top=0,left=0,resizable=no, status=no, directories=no, addressbar=no, toolbar=no, scrollbars=no, menubar=no, location=no, statusbar=no");
}