(ibuffer-formats): Doc fix.
(ibuffer-mode-map): Bind <up> to `ibuffer-backward-line'. Bind
new functions from ibuf-ext.el. Add menu entries for them.
Remove superfluous tooltips.
(ibuffer-toggle-marks): If on a group name, then toggle marks just
in that group.
(ibuffer-mark-interactive): Handle filter groups.
(ibuffer-mark-forward, ibuffer-unmark-forward)
(ibuffer-mark-for-delete, ibuffer-unmark-backward)
(ibuffer-mark-for-delete-backwards): Update docs.
(ibuffer-current-filter-groups): Moved to ibuf-ext.el, and renamed
to `ibuffer-current-filter-groups-with-position'.
(ibuffer-redisplay-engine): Handle
`ibuffer-show-empty-filter-groups'.
(ibuffer-mode): Add some documentation about filter groups.