private void mantenimientoModeloDeVehiculoToolStripMenuItem_Click(object sender, EventArgs e)
 {
     if (modeloVehiculocs == null)
     {
         modeloVehiculocs             = new ModeloVehiculocs();
         modeloVehiculocs.MdiParent   = this;
         modeloVehiculocs.FormClosed += new FormClosedEventHandler(cerrarModelo);
         modeloVehiculocs.Show();
     }
     else
     {
         modeloVehiculocs.Activate();
     }
 }
 private void cerrarModelo(object sender, FormClosedEventArgs e)
 {
     modeloVehiculocs = null;
 }