(name_next): Go back to using plain chdir.

(name_next): Go back to using plain chdir.
(name_gather): Use chdir_arg to keep track of arguments to chdir.
(addname): Likewise.
(name_match): Use chdir_do to act on chdir args.
(merge_sort): Moved here from incremen.c.
(compare_names, add_hierarchy_to_namelist, collect_and_sort_names):
Likewise.
(name_expand): Remove.
(name_from_list): Skip fack names.
Use chdir_do to act on chdir args.
(struct avoided_name): New struct.
(avoided_names): New var.
(add_avoided_name, is_avoided_name): New functions.