* elmo-shimbun.el (elomo-shimbun-folder): Added entity-hash slot.

* elmo-shimbun.el (elomo-shimbun-folder): Added entity-hash slot.
(elmo-shimbun-folder-entity-hash): New function.
(elmo-shimbun-folder-shimbun-header): Ditto.
(elmo-shimbun-entity-to-header): Ditto.
(elmo-shimbun-msgdb-to-headers): Removed.
(elmo-shimbun-folder-setup): Ditto.
(elmo-shimbun-folder-header-hash-setup): Don't use x-shimbun-id
for hash key.
(elmo-shimbun-get-headers): Set new headers only to slot. Don't
call `elmo-shimbun-folder-header-hash-setup' if headers is nil.
Removed useless local bind.
(elmo-folder-open-internal): Don't call
`elmo-shimbun-folder-setup'.
(elmo-folder-close-internal): Clear entity-hash slot.
(elmo-folder-clear): Ditto.
(elmo-shimbun-msgdb-create-entity): Use
`elmo-shimbun-folder-shimbun-header'.
(elmo-map-message-fetch): Ditto.
(elmo-shimbun-update-overview): Use overview entity instead of
shimbun header to lookup id by references.
(elmo-map-folder-list-message-locations): Use not only headers but
also overviews to list locations.