(ibuffer-filter-group-name-face): New.

(ibuffer-filter-group-name-face): New.
(ibuffer-mode-map): Bind and add menu entries for most new
functions; also, bind the arrow keys to the movement functions.
(ibuffer-mode-filter-group-map): New.
(ibuffer-mouse-toggle-mark): Handle group names.
(ibuffer-mouse-visit-buffer): Error if the current buffer is
killed.
(ibuffer-skip-properties): New function.
(ibuffer-backward-line, ibuffer-forward-line): Optionally skip
group names.  Also, handle new properties.
(ibuffer-visit-buffer, ibuffer-visit-buffer-other-window): Move
error handling to `ibuffer-current-buffer'.
(ibuffer-visit-buffer-other-frame, ibuffer-bury-buffer): Ditto.
(ibuffer-visit-tags-table, ibuffer-do-view-1): Ditto.
(ibuffer-toggle-marks): Add optional group argument.
(ibuffer-mark-interactive): Skip group names.
(ibuffer-current-buffer): Clean up error handling.
(ibuffer-fontify-region-function): Fontify group names.
(ibuffer-map-lines): Add extra group argument.  Handle it.
(ibuffer-current-filter-groups): New function.
(ibuffer-redisplay): Handle hidden filtering groups.
(ibuffer-sort-bufferlist): New function, taken from
`ibuffer-insert-buffers-and-marks'.
(ibuffer-insert-filter-group): New function.
(ibuffer-redisplay-engine): Renamed from
`ibuffer-insert-buffers-and-marks'.  Handle new filtering groups.
(ibuffer): Add filter-groups argument.  Handle it.  Use
`save-selected-window'.
(ibuffer-mode): Make `ibuffer-filtering-groups' and
`ibuffer-hidden-filtering-groups' buffer-local.