support old qt versions < 5.6

src/testgui.hxx

@@ -38,7 +38,9 @@ class TestGUI: public QMainWindow, protected Ui::TestGUI {
         _inEventFilter(false) {
       setWindowTitle("[*]");
       setupUi(this);
+      #if QT_VERSION >= 0x050600
       setDockOptions(dockOptions()|QMainWindow::GroupedDragging);
+      #endif
       menuViews->addAction(_setupScriptDock->toggleViewAction());
       menuViews->addAction(_scriptCommandsDock->toggleViewAction());
       menuViews->addAction(_domDock->toggleViewAction());