Where is member-if defined?

[John Daschbach <jldasch@3-cities.com>]

I finally got imap support working in gnus but after one use it's
broken.  The initial problem was that I defined 

(setq nnimap-debug (not nil))

which breaks imap support and which took me forever to track down.  Even
with debug-on-error set true I couldn't figure where the error was
occuring, just that I got an illegal type error.  I still haven't fixed
that problem, just turned off debugging.

Now, I get an undefined function 'member-if' which occurs in the
following fragment in nnimap.el

(or (member-if (lambda (mailbox)
			   (string= (downcase mailbox) "\\noselect"))
			 (imap-mailbox-get 'list-flags mbx
					   nnimap-server-buffer))

I've grepped both the gnus (9 Feb 2000 CVS update) and Emacs (20.3) lisp
directories and this is in fact the only reference to this function in
any of these locations.

So what should I do?  I'd really like to get imap working in gnus.

-John