Fix how configuration tables and empdump treat omitted entries

Fix how configuration tables and empdump treat omitted entries

Change xundump to blank out omitted rows.  Before, they were left
alone.  Impact:

* No change for reading builtin tables.

* Reading custom tables now replaces the builtin tables instead of
  sort-of-merging them.  Wasn't a real merge, because it dropped
  builtin entries after the last custom entry, except for
  non-truncatable tables item, sect-chr and infrastructure.

* empdump -i now replaces the old state instead of sort-of-merging the
  dump into the old state.  Wasn't a real merge, because it dropped
  old state entries after the last entry in the dump, except for the
  fixed-size tables sect, nat, realm and game.