Merge branch 'master' into jgrpp

# Conflicts:
#	src/airport_gui.cpp
#	src/build_vehicle_gui.cpp
#	src/direction_type.h
#	src/gfx_type.h
#	src/group_gui.cpp
#	src/misc_gui.cpp
#	src/rail_gui.cpp
#	src/road_gui.cpp
#	src/signs_gui.cpp
#	src/slope_func.h
#	src/smallmap_gui.cpp
#	src/terraform_gui.cpp
#	src/toolbar_gui.cpp
#	src/town_gui.cpp
#	src/town_type.h
#	src/vehicle_type.h
#	src/widget_type.h

src/vehicle_gui.h

@@ -22,12 +22,13 @@
 void ShowVehicleRefitWindow(const Vehicle *v, VehicleOrderID order, Window *parent, bool auto_refit = false, bool is_virtual_train = false);
 
 /** The tabs in the train details window */
-enum TrainDetailsWindowTabs {
+enum TrainDetailsWindowTabs : byte {
 	TDW_TAB_CARGO = 0, ///< Tab with cargo carried by the vehicles
 	TDW_TAB_INFO,      ///< Tab with name and value of the vehicles
 	TDW_TAB_CAPACITY,  ///< Tab with cargo capacity of the vehicles
 	TDW_TAB_TOTALS,    ///< Tab with sum of total cargo transported
 };
+DECLARE_ENUM_AS_ADDABLE(TrainDetailsWindowTabs)
 
 /** Special values for vehicle-related windows for the data parameter of #InvalidateWindowData. */
 enum VehicleInvalidateWindowData {