function llamarasincrono(url, id_contenedor){
//document.getElementById(id_contenedor).innerHTML="<br/><br/><center><img src='images/div_info.png' alt=''/> Espere, cargando...</center>";
var pagina_requerida = false
if (window.XMLHttpRequest) {
pagina_requerida = new XMLHttpRequest()
} else if (window.ActiveXObject){
try {
pagina_requerida = new ActiveXObject("Msxml2.XMLHTTP")
} 
catch (e){ 
try{
pagina_requerida = new ActiveXObject("Microsoft.XMLHTTP")
}
catch (e){}
}
}
else
return false
pagina_requerida.onreadystatechange=function(){ 
cargarpagina(pagina_requerida, id_contenedor)
}
pagina_requerida.open('GET', url, true) 
pagina_requerida.send(null)
}

function cargarpagina(pagina_requerida, id_contenedor){
if (pagina_requerida.readyState == 4 && (pagina_requerida.status==200 || window.location.href.indexOf("http")==-1))
if(pagina_requerida.responseText.length>0)document.getElementById(id_contenedor).innerHTML=pagina_requerida.responseText
}