Commentary: Add text.

Commentary: Add text.

History: Add header and mbox item.

Overhaul summary buffer movement.

(rmail-summary-font-lock-keywords): Compress the attribute character
display field by one character.

(rmail-new-summary): Rewrite.

(rmail-make-summary-line-1): Slight rewrite to deal with small changes
in the summary format.

(rmail-make-basic-summary-line): Use the rmail message vector.

(rmail-summary-next-msg): Rewrite.

(rmail-summary-next-labeled-message): Set the summary buffer copy of
the rmail-current-message to force the display to show it.

(rmail-summary-next-same-subject): Rewrite.

(rmail-summary-delete-forward): Remove some questionable code and make
summary buffer movement explicit.

(rmail-summary-mark-deleted): Make sure to reflect the deletion for
the Rmail buffer.

(rmail-summary-deleted-p): Rewrite.

(rmail-summary-undelete-many): Set the summary buffer copy of
the rmail-current-message to force the display to show it.

(rmail-summary-rmail-update): Rewrite.

(rmail-summary-mode-map): Use "B" to send the message body to a
browser; use (rmail-summary-output) instead of
(rmail-summary-output-to-rmail-file).  Similarly for the menu item.

(rmail-summary-mouse-goto-msg): Set the summary buffer copy of the
rmail-current-message to force the display to show it.

(rmail-summary-get-message-at-point): New function.

(rmail-summary-goto-msg): Rewrite.

(rmail-summary-expunge, rmail-summary-expunge-and-save,
rmail-summary-get-new-mail, rmail-summary-toggle-header): Rewrite.

(rmail-summary-get-line-count, rmail-summary-get-summary-attributes,
rmail-summary-get-summary, rmail-summary-update-attribute,
rmail-summary-browse-body): New functions.