/// <summary>
        /// User clicks on "update".
        /// </summary>
        /// <param name="sender">ignored</param>
        /// <param name="e">ignored</param>
        private void btnUpdateCheck_Click(object sender, EventArgs e)
        {
            // check if an error is possible
            Update u = new Update(false, this);
            if (u.hadErrors)
                return;

            // update available?
            if (u.checkUpdate())
            {

                // open url, if the user wants
                if (RTLMessageBox.Show(this,
                    Program.res.GetString("BOX_UpdateInformation")
                    .Replace("%s", u.getVersion()),
                    MessageBoxButtons.YesNoCancel,  
                    MessageBoxDefaultButton.Button1,
                    MessageBoxIcon.Information)
                    == DialogResult.Yes)

                    openUrl(u.getUpdateUrl());
            }

            // no update found
            else 
                RTLMessageBox.Show(this,
                    Program.res.GetString("BOX_UpdateNone"),
                    MessageBoxIcon.Information);
        }