//Aquesta funcio ens obra una URL donada en forma de popup amb una amplada (w) i una alçada (h)
function popUpCentrat(url,w,h){
	t=(screen.availHeight/2)-(h/2)-100;
	l=(screen.availWidth/2)-(w/2);
	param = "width="+w+"px,";
	param += "height="+h+"px,";
	param += "top="+t+",";
	param += "left="+l+",";
	param += "menubar=no,"
	param += "toolbar=no,"
	param += "resizable=no,"
	param += "scrollbars=yes"
	window.open(url,"abreviacions",param);
}