Biff support.

Biff support.

* wl/wl.el (wl): Call `wl-biff-start'.
(wl-exit): Call `wl-biff-stop'.
(wl-plugged-mode): Show biff in modeline.
(wl-unplugged-glyph, wl-unplugged-glyph): Removed.

* wl/wl-xmas.el (wl-draft-overload-functions): Show biff in modeline.
(wl-biff-init-icons): New function.
(wl-plugged-init-icons): Don't make too much keymaps.
(wl-biff-nomail-glyph, wl-biff-mail-glyph): New variables.

* wl/wl-vars.el (wl-biff-nomail-icon, wl-biff-mail-icon,
wl-biff-state-indicator-off, wl-biff-state-indicator-on): New variables.
(wl-biff-check-interval, wl-biff-check-folder-list): New user options.

* wl/wl-util.el (wl-biff-check-folders, wl-biff-event-handler, wl-biff-start,
wl-biff-stop): New functions.
(timer-next-integral-multiple-of-time): Defined with `defun-meybe'.
(wl-biff-timer-name): New variable.

* wl/wl-summary.el (wl-summary-mode): Show biff in modeline.

* wl/wl-nemacs.el (wl-draft-overload-functions): Show biff in modeline.
(wl-plugged-init-icons, wl-folder-init-icons): Removed.

* wl/wl-mule.el (wl-draft-overload-functions): Show biff in modeline.
(wl-plugged-init-icons, wl-folder-init-icons): Removed.

* wl/wl-folder.el (wl-make-plugged-alist): Call `wl-biff-init-icons'.
(TopLevel): Bind `wl-biff-init-icons', `wl-plugged-init-icons' and
`wl-folder-init-icons' to `ignore' if they are not available.
(wl-folder-mode): Show biff in modeline.

* wl/wl-e21.el (wl-draft-overload-functions): Show biff in modeline.
(wl-biff-init-icons): New function.
(wl-plugged-init-icons): Don't make too much keymaps.
(wl-biff-nomail-image, wl-biff-mail-image): New variables.

* etc/icons/letter.xpm, etc/icons/no-letter.xpm: New files.