(rmail-insert-inbox-text): Detect locked

(rmail-insert-inbox-text): Detect locked
RMAIL files at the outset, before copying any files.

(rmail-find-all-files): Eliminate recursive scan.  Rely on directory-files
to do the filtering.

(rmail-convert-to-babyl-format):
Increase sit-for timeout to 3 seconds.

(rmail-get-new-mail): Handle files in multiple batches,
in case two inboxes have the same last name component.

(rmail-show-message): Bind `end' after clearing the
"unseen" attribute.

(rmail-show-message): Clear `unseen' even if header
is already reformatted--but don't do it if rmail-not-really-seen.
(rmail-not-really-seen): New variable.