bug#6830: widget-complete bad completions in :type 'file

[Lennart Borgman]

I get bad completion alternatives in Custom for a field of type
"file". It looks like it takes the files in the current directory and
disregards the contents of the field.

To see it start from "emacs -Q" and evaluate

(defcustom pause-later-file "~/.emacs-pause-later"
  "File for storing pauses to do later."
  :type 'file
  :group 'pause-yoga)

Then do "M-x customize-option" to customize it. Go to the file field,
enter some text and do "M-x widget-complete" (the only way to complete
it in an unpatched Emacs on w32).

With a trunk checkout from 2010-08-04 on w32.
I get a list of the file in the current dir.