(subst.in): Substitute it. Fix prerequisites.
(read_builtin_tables): New.
(main): Call it. This doesn't do anything, because no builtin tables
have been defined.
(config_tables): New econfig key.
(read_config_tables): New, implements config_tables.
(main): Call it. Need to call ef_init() and chdir(configdir) first.
(ef_init_srv): Don't call ef_init(), since main() did it already.
Remove old way to do the same:
(ef_load): Remove, along with calls.
(empfile): Set configuration tables' member file back to NULL.
