(ibuffer-mode-operate-menu, ibuffer-mode-mark-menu)

(ibuffer-mode-operate-menu, ibuffer-mode-mark-menu)
(ibuffer-mode-view-menu): Unused variables; deleted.
(ibuffer-find-file): Pass wildcard flag to `find-file' correctly.
(ibuffer-mode-groups-popup): New variable.
(toplevel): Bind filter group menu entries in it.  Add :enable
forms for some menu items.
(toplevel): Bind [down-mouse-3] in `ibuffer-mode-filter-group-map'
to `ibuffer-mouse-popup-menu'.
(ibuffer-mouse-popup-menu): Test whether or not we're on a filter
group name, and if so, pop up a filter group menu.