//função que abre um popup
function popup(url)
{
	var win = window.open(url, "popup", "top=0, left=0, width=900, height=310");
	
	var tam1 = (window.screen.availWidth / 2) - (win.document.body.offsetWidth / 2) - (window.screen.availWidth * 0.01);
	var tam2 = (window.screen.availHeight / 2) - (win.document.body.offsetHeight / 2) - (window.screen.availHeight * 0.062);

	win.moveTo(tam1, tam2); 
}