message: Insight: Put single/dual column actions in a QActionGroup to ensure they cannot both be unchecked.
diff: #include "DirWidget2.h"
  #include "ui_DirWidget2.h"
  +#include <QActionGroup>
  #include <QMessageBox>
  #include <QCursor>
  #include <QClipboard>
  @@ -44,9 +45,12 @@ DirWidget::DirWidget(QString objID, QWidget *parent) : QWidget(parent), ui(new U
  line_dir = new QLineEdit(this);
  toolbar->addWidget(line_dir);
  connect(line_dir, SIGNAL(returnPressed()), this, SLOT(dir_changed()) );
  + QActionGroup *columnActionGroup = new QActionGroup(this);
  toolbar->addAction(ui->actionSingleColumn);
  ui->actionSingleColumn->setChecked(true);
  + columnActionGroup->addAction(ui->actionSingleColumn);
  toolbar->addAction(ui->actionDualColumn);
  + columnActionGroup->addAction(ui->actionDualColumn);
  toolbar->addAction(ui->actionMenu);
  //Add the browser widgets
  RCBW = 0; //right column browser is unavailable initially
  @@ -400,7 +404,6 @@ void DirWidget::dir_changed(){
  void DirWidget::on_actionSingleColumn_triggered(bool checked){
  if(!checked){ return; }
  - ui->actionDualColumn->setChecked(false);
  if(RCBW==0){ return; } //nothing to do
  ui->browser_layout->removeWidget(RCBW);
  RCBW->deleteLater();
  @@ -410,7 +413,6 @@ void DirWidget::on_actionSingleColumn_triggered(bool checked){
  void DirWidget::on_actionDualColumn_triggered(bool checked){
  if(!checked){ return; }
  - ui->actionSingleColumn->setChecked(false);
  if(RCBW!=0){ return; } //nothing to do
  RCBW = new BrowserWidget("rc", this);
  ui->browser_layout->addWidget(RCBW);
  