Fixed faked transparency of folding makers with Plastique style

Plastique is manually blending with the background color, so make sure
we set the background to the highlight color when the folding marker is
hovered.

src/plugins/texteditor/basetexteditor.h

@@ -511,8 +511,11 @@ private:
     void moveLineUpDown(bool up);
     void saveCurrentCursorPositionForNavigation();
 
-    void drawFoldingMarker(QPainter *painter, const QRect &rect,
-                           bool expanded, bool hovered) const;
+    void drawFoldingMarker(QPainter *painter, const QPalette &pal,
+                           const QRect &rect,
+                           bool expanded,
+                           bool active,
+                           bool hovered) const;
 
     void toggleBlockVisible(const QTextBlock &block);
     QRect collapseBox();