Fix remaining issues with mapgen scriptapi

src/objdef.h

@@ -66,6 +66,7 @@ protected:
 // WARNING: Ownership of ObjDefs is transferred to the ObjDefManager it is
 // added/set to.  Note that ObjDefs managed by ObjDefManager are NOT refcounted,
 // so the same ObjDef instance must not be referenced multiple
+// TODO: const correctness for getter methods
 class ObjDefManager {
 public:
 	ObjDefManager(IGameDef *gamedef, ObjDefType type);