Lua struct obj improvements

If the core frees the obj struct referred by lua, don't free it,
just mark it as OBJ_LUAFREE - lua will free it in gc once all
the references to it are gone.

include/patchlevel.h

@@ -14,7 +14,7 @@
  * Incrementing EDITLEVEL can be used to force invalidation of old bones
  * and save files.
  */
-#define EDITLEVEL 7
+#define EDITLEVEL 8
 
 #define COPYRIGHT_BANNER_A "NetHack, Copyright 1985-2019"
 #define COPYRIGHT_BANNER_B \