private void gestionClienteToolStripMenuItem_Click(object sender, EventArgs e)
        {
            if (formGestionCliente == null)
            {
                formGestionCliente             = new FormGestionCliente();
                formGestionCliente.MdiParent   = this;
                formGestionCliente.FormClosed += new FormClosedEventHandler(formCliente_FormClosed);

                formGestionCliente.Show();
            }
            else
            {
                formGestionCliente.Activate();
            }
        }
 private void formCliente_FormClosed(object sender, FormClosedEventArgs e)
 {
     formGestionCliente = null;
 }