emacs -q
M-x ffap-bindings
C-xC-f .r TAB

(or any other prefix while trying to complete a filename in the
minibuffer) gives an error because completion-embedded-envvar-table is
an 'undefined function'. Here's the backtrace:

Debugger entered--Lisp error: (void-function completion-embedded-envvar-table)
  completion-embedded-envvar-table(#("~/.r" 0 2 (auto-composed t) 2 3 (auto-composed t) 3 4 (auto-composed t)) "~/" nil)
  try-completion(#("~/.r" 0 2 (auto-composed t) 2 3 (auto-composed t) 3 4 (auto-composed t)) completion-embedded-envvar-table "~/")
  complete-with-action(nil completion-embedded-envvar-table #("~/.r" 0 2 (auto-composed t) 2 3 (auto-composed t) 3 4 (auto-composed t)) "~/")
  #[(G88405 G88406 string pred action) "Å	J\n$†Å\fJ\n$‡" [action G88406 string pred G88405 complete-with-action] 5](--b-- --a-- #("~/.r" 0 2 (auto-composed t) 2 3 (auto-composed t) 3 4 (auto-composed t)) "~/" nil)
  apply(#[(G88405 G88406 string pred action) "Å	J\n$†Å\fJ\n$‡" [action G88406 string pred G88405 complete-with-action] 5] --b-- --a-- (#("~/.r" 0 2 (auto-composed t) 2 3 (auto-composed t) 3 4 (auto-composed t)) "~/" nil))
  read-file-name-internal(#("~/.r" 0 2 (auto-composed t) 2 3 (auto-composed t) 3 4 (auto-composed t)) "~/" nil)
  ffap-read-file-or-url-internal(#("~/.r" 0 2 (auto-composed t) 2 3 (auto-composed t) 3 4 (auto-composed t)) "~/" nil)
  try-completion(#("~/.r" 0 2 (auto-composed t) 2 3 (auto-composed t) 3 4 (auto-composed t)) ffap-read-file-or-url-internal "~/")
  minibuffer--do-completion()
  minibuffer-complete()
  call-interactively(minibuffer-complete nil nil)
  completing-read("Find file or URL: " ffap-read-file-or-url-internal "~/" nil ("~/" . 2) (file-name-history) nil)
  ffap-read-file-or-url("Find file or URL: " nil)
  byte-code("ƒ	Â\nÄ	†Å ‰‰ƒÆ ˆ\"‡" [ffap-url-regexp guess ffap-read-file-or-url "Find file or URL: " "Find file: " ffap-guesser ffap-highlight] 4)
  ffap-prompter()
  find-file-at-point()
  call-interactively(find-file-at-point nil nil)



In GNU Emacs 23.0.60.2 (i686-pc-linux-gnu)
 of 2008-04-12 on rivendell
configured using `configure  '--without-x' '--enable-maintaner-mode''

Important settings:
  value of $LC_ALL: nil
  value of $LC_COLLATE: nil
  value of $LC_CTYPE: nil
  value of $LC_MESSAGES: nil
  value of $LC_MONETARY: nil
  value of $LC_NUMERIC: nil
  value of $LC_TIME: nil
  value of $LANG: en_US.UTF-8
  value of $XMODIFIERS: nil
  locale-coding-system: utf-8-unix
  default-enable-multibyte-characters: t

Major mode: Debugger

Minor modes in effect:
  menu-bar-mode: t
  file-name-shadow-mode: t
  global-font-lock-mode: t
  font-lock-mode: t
  global-auto-composition-mode: t
  auto-composition-mode: t
  auto-compression-mode: t
  line-number-mode: t
  transient-mark-mode: t

Recent input:
ESC x f f a p TAB p TAB DEL DEL p - b TAB RET C-x C-f 
. e TAB C-g ESC x t o o g DEL DEL g g l e - d e TAB 
e r TAB RET C-x C-f . r TAB C-p C-@ C-n C-n C-n C-n 
C-n C-n C-n C-n C-n C-n C-n C-n C-n C-n C-n C-n C-n 
C-n ESC w C-g ESC x r e p o r TAB RET

Recent messages:
("emacs" "-q")
For information about GNU Emacs and the GNU system, type C-h C-a.
try-completion: Symbol's function definition is void: completion-embedded-envvar-table
Quit
Debug on Error enabled globally
Entering debugger...
Quit