bug#8804: Creating ibuffer named filters via / g doesn't work

[Noam Postavsky]

emacs-version:
GNU Emacs 23.3.1 (x86_64-unknown-linux-gnu, GTK+ Version 2.24.4) of
2011-06-04 on localhost

Steps to reproduce from emacs -Q:

M-x ibuffer RET
/ n sc RET
/ g foo RET

The filter group named foo is NOT created as expected.

I believe this is caused by the fix for bug#7969, which changed the
definition for ibuffer-filter-disable. After evaluating the old
definition, namely:

(defun ibuffer-filter-disable ()
  "Disable all filters currently in effect in this buffer."
  (interactive)
  (setq ibuffer-filtering-qualifiers nil
        ) ;ibuffer-filter-groups nil
  (let ((buf (ibuffer-current-buffer)))
    (ibuffer-update nil t)
    (when buf
      (ibuffer-jump-to-buffer (buffer-name buf)))))

The above procedure results in a filter group named foo. The new
definition sets ibuffer-filter-groups to nil as well, which is a problem
because ibuffer-filters-to-filter-group ends by calling it.