* elmo.el (elmo-folder-creatable-p): Changed default value to nil

* elmo.el (elmo-folder-creatable-p): Changed default value to nil
from t.

* elmo-pop3.el (elmo-folder-exists-p): Return nil if unplugged.

* elmo-nntp.el (elmo-folder-exists-p-plugged): Divided plugged
case from `elmo-folder-exists-p'.
(elmo-folder-exists-p): Removed.
(elmo-folder-creatable-p) Ditto.

* elmo-net.el (elmo-folder-create): Defined.
(elmo-folder-create-unplugged): New function.
(elmo-folder-exists-p): Changed default value to nil from t.

* elmo-imap4.el (elmo-folder-creatable-p): Defined.
(elmo-folder-create-plugged): Renamed from `elmo-folder-create'.

* elmo-dop.el (elmo-folder-create-dop): Renamed from
`elmo-create-folder-dop' and append queue
'elmo-folder-create-dop-delayed instead of 'elmo-folder-create.
(elmo-folder-create-dop-delayed): New function.

* elmo-cache.el (elmo-folder-creatable-p): Ditto.

* elmo-shimbun.el (elmo-folder-creatable-p): Ditto.

* elmo-sendlog.el (elmo-folder-creatable-p): Ditto.
(elmo-folder-writable-p) : Ditto.

* wl-summary.el (wl-summary-refile-subr): Cause an error if FOLDER
is not writable.

* wl-folder.el (wl-folder-create-subr): Cause an error if FOLDER
is not creatable.