bugfix for issue #569: thumbs disappear when +/- button is pressed

An implementation for redrawNeed() was lacking in the derived class BatchQueue:
when updateImage called it there was no effect.

rtgui/filebrowser.h

@@ -116,7 +116,6 @@ class FileBrowser  : public ThumbBrowserBase, public LWButtonListener {
 
     void openDefaultViewer (int destination);
 
-    void redrawNeeded (ThumbBrowserEntryBase* entry);
     void thumbRearrangementNeeded ();
     void _thumbRearrangementNeeded ();