FindTrackRect omits all margins; better screen reader focus rects...

... Formerly it was outside of the yellow focus at the right side.  Now it
follows the yellow consistently on four sides.

The constant dx in TrackPanelAx::GetLocation might be adjusted.

No change of behavior is intended at other uses of FindTrackRect

src/TrackPanel.h

@@ -563,6 +563,9 @@ protected:
    };
    virtual FoundCell FindCell(int mouseX, int mouseY);
 
+   // If label, rectangle includes track control panel only.
+   // If !label, rectangle includes all of that, and the vertical ruler, and
+   // the proper track area.
    virtual wxRect FindTrackRect(Track * target, bool label);
 
    virtual int GetVRulerWidth() const;