Merge branch 'master' into jgrpp

# Conflicts:
#	regression/regression/result.txt
#	src/autoreplace_cmd.cpp
#	src/industry_gui.cpp
#	src/landscape.cpp
#	src/network/network_content.cpp
#	src/newgrf_roadstop.cpp
#	src/pathfinder/yapf/yapf_ship.cpp
#	src/road_gui.cpp
#	src/saveload/ai_sl.cpp
#	src/saveload/saveload.h
#	src/saveload/vehicle_sl.cpp
#	src/station.cpp
#	src/station_gui.cpp
#	src/video/cocoa/cocoa_ogl.h
#	src/video/sdl2_opengl_v.h
#	src/video/video_driver.hpp
#	src/video/win32_v.h
#	src/widget_type.h
#	src/widgets/dropdown.cpp
#	src/widgets/dropdown_type.h
#	src/window.cpp

src/widget_type.h

@@ -520,6 +520,9 @@ public:
 	int shown_plane; ///< Plane being displayed (for #NWID_SELECTION only).
 	const WidgetID index; ///< If non-negative, index in the #Window::widget_lookup.
 	bool independent_planes = false; ///< If true, treat planes as independent for layout purposes.
+
+private:
+	WidgetLookup *widget_lookup; ///< Window's widget lookup, updated in SetDisplayedPlane().
 };
 
 /** Nested widget container flags, */