* elmo.el (elmo-folder-append-buffer): Changed argument from unread

* elmo.el (elmo-folder-append-buffer): Changed argument from unread
to flag. (All other related portions are changed.)
(elmo-folder-msgdb-create): Likewise.
(elmo-generic-folder-append-messages): Use flag-table instead of seen-list.
(elmo-folder-move-messages): Removed redundant process.
(elmo-folder-synchronize): Likewise.

* elmo-msgdb.el (elmo-flag-table-get): New function.
(elmo-flag-table-save): Fixed.
(elmo-msgdb-length): New inline function.
(elmo-msgdb-flag-table): New function.
(elmo-msgdb-mark): Add optional argument new.
(elmo-msgdb-add-msgs-to-seen-list): Abolish.
(elmo-msgdb-seen-list): Ditto.
(elmo-msgdb-add-msgs-to-seen-list): Ditto.