* elmo-util.el (elmo-progress-start): Accept nil for `total'. Set

* elmo-util.el (elmo-progress-start): Accept nil for `total'.  Set
`elmo-progress-counter' as t when a query callback returns nil.
(elmo-progress-clear): New function.
(elmo-progress-done): Split into `elmo-progress-clear'.
(elmo-progress-notify): Update a total slot when it is nil.
(elmo-with-progress-display): Call `elmo-progress-clear' in
unwind-protect and move calling `elmo-progress-done' to outside.

* elmo-imap4.el (elmo-imap4-find-next-line): Call
`elmo-progress-notify' with :total parameter instead of
`elmo-progress-counter-set-total'.