object deletion during save operations

Not sure why my earlier attempt was unsuccessful.  This one isn't as
comprehensive but is simpler and better yet, works as intended.

When saving a level or exiting the program, objects can be deleted
directly rather than having to pass though the objs_deleted list.

include/hack.h

@@ -794,6 +794,7 @@ struct sinfo {
     int exiting;                /* an exit handler is executing */
     int saving;                 /* creating a save file */
     int restoring;              /* reloading a save file */
+    int freeingdata;            /* in saveobjchn(), mode FREEING */
     int in_getlev;              /* in getlev() */
     int in_moveloop;            /* normal gameplay in progress */
     int in_impossible;          /* reporting a warning */