* elmo.el (elmo-folder): Add new slot `flag-table'.

* elmo.el (elmo-folder): Add new slot `flag-table'.
(elmo-folder-flag-table): New API.
(elmo-folder-close-flag-table): Ditto.
(elmo-folder-preserve-falgs): New function.
(elmo-generic-folder-append-messages): Use
`elmo-folder-flag-table' and `elmo-folder-close-flag-table'.
Flag of a non-registered message, it sets to nil.
Does not set flag to flag-table.

* elmo-maildir.el (elmo-folder-append-buffer): Use
`elmo-folder-preserve-falgs'.
(elmo-folder-append-messages): Use `elmo-folder-flag-table' and
`elmo-folder-close-flag-table'.

* elmo-archive.el (elmo-folder-append-buffer): Fix interface.
(elmo-archive-folder-append-buffer): Use
`elmo-folder-preserve-falgs'.

* elmo-cache.el (elmo-folder-append-buffer): Ditto.

* elmo-imap4.el (elmo-folder-append-buffer): Ditto.

* elmo-localdir.el (elmo-folder-append-buffer): Ditto.
(elmo-folder-append-messages): Use `elmo-folder-flag-table' and
`elmo-folder-close-flag-table'.