Add setting to control autosave interval mode

src/settings_type.h

@@ -177,6 +177,7 @@ struct GUISettings : public TimeSettings {
 	ZoomLevel zoom_max;                      ///< maximum zoom out level
 	ZoomLevel sprite_zoom_min;               ///< maximum zoom level at which higher-resolution alternative sprites will be used (if available) instead of scaling a lower resolution sprite
 	uint32 autosave_interval;                ///< how often should we do autosaves?
+	bool   autosave_realtime;                ///< autosaves based on real elapsed time (with pause handling)
 	bool   threaded_saves;                   ///< should we do threaded saves?
 	bool   keep_all_autosave;                ///< name the autosave in a different way
 	bool   autosave_on_exit;                 ///< save an autosave when you quit the game, but do not ask "Do you really want to quit?"