function actualiza_dias(cmbDias, cmbMeses, cmbAnos) {
	var cant_dias = new Array(31, 28, 31, 30, 31, 30, 31, 31, 30, 31, 30, 31);
	var cant, i, old;
	if(es_bisiesto(cmbAnos.value))
		cant_dias[1] = 29;
	if(cmbMeses.value == "")
		cant = 31;
	else
		cant = cant_dias[cmbMeses.value - 1];
	old = cmbDias.selectedIndex;
	cmbDias.length = cant + 1;
	cmbDias.selectedIndex = old;
	cmbDias[0].text = "-";
	cmbDias[0].value = "";
	for(i=1; i<=cant; i++) {
		cmbDias[i].text = i;
		cmbDias[i].value = i;
	}
}

function es_bisiesto(ano) {
	if(ano % 400 == 0)
		return true;
	else {
		if(ano % 100 == 0)
			return false;
		else {
			if(ano % 4 == 0)
				return true;
			else
				return false;
		}
	}
}