* elmo.el (elmo-folder-list-importants): Rewirte. Use global mark

* elmo.el (elmo-folder-list-importants): Rewirte. Use global mark
instead of current mark.

* elmo-multi.el (elmo-folder-list-importants-internal): No
operation if importants is not list.

* elmo-filter.el (elmo-filter-folder-list-importants-internal):
Return t if importants is not list.

* elmo-map.el (elmo-map-folder-list-importants): Define.
(elmo-folder-list-importants-internal): Check return value of
`elmo-map-folder-list-importants-internal'.

* elmo-cache.el (elmo-folder-list-importants-internal): Eliminated.

* elmo-mark.el (elmo-folder-list-importants-internal): Ditto.

* elmo-nmz.el (elmo-folder-list-importants-internal): Ditto.

* elmo-shimbun.el (elmo-folder-list-importants-internal): Ditto.