Document tables EF_COMM, EF_TRADE and EF_COUNTRY have an owner

xdvisible() relies on that.

Set EFF_OWNER in the table definitions.  EFF_OWNER is not actually
used right now, so this doesn't fix anything broken.

include/commodity.h

@@ -41,9 +41,11 @@
 #include "item.h"
 
 struct comstr {
+    /* initial part must match struct empobj */
     short ef_type;
     natid com_owner;
     short com_uid;
+    /* end of part matching struct empobj */
     i_type com_type;
     int com_amount;
     float com_price;