(nxtitemp, trade_getitem, trade_desc, trade_check_item_ok, nxtitem,

oprange, show_mission, nameofitem, build_mission_list_type,
unit_map, xdvisible, trdswitchown, ontradingblock, trad, check_trade,
unit_type_name, start_stop_unit, scut, scra, mission, multifire,
perform_mission, fuel, NSC_GENITEM): Replace struct genitem with
struct empobj.  Remove genitem.h and create a new file empobj.h.
Replace multiple instances of unions of ef_type structures with
one standard union empobj_storage which is a superset of the individual
instances.

include/file.h

@@ -72,7 +72,7 @@ struct empfile {
 /*
  * EFF_XY / EFF_OWNER / EFF_GROUP assert that coordinates / owner /
  * group of such a table's entries can be safely obtained by
- * dereferencing entry address cast to struct genitem *.
+ * dereferencing entry address cast to struct empobj *.
  */
 #define EFF_XY		bit(0)
 #define EFF_OWNER	bit(1)