private void buttonAltaEditar_Click(object sender, EventArgs e)
        {
            FormAltaCliente fac = new FormAltaCliente();

            fac.ShowDialog();
            if (fac.DialogResult == DialogResult.OK)
            {
                comboBoxClientes.DataSource = clientes.GetExistentes();
            }
        }
        private void buttonAltaCliente_Click(object sender, EventArgs e)
        {
            FormAltaCliente c = new FormAltaCliente();

            c.ShowDialog();
        }