(elmo-folder-initialize): Setup `dir-name' slot.
(elmo-archive-folder-list-subfolders): Fixed problem when `name' is "".
Use `dir-name' as prefix of each subfolders.
+ (Applyed patch from Takaaki MORIYAMA <taka@arcadia.co.jp>)
2001-12-13 Hiroya Murata <lapis-lazuli@pop06.odn.ne.jp>