bug#8256: widget-complete does not complete for type 'directory on w32

[Stefan Monnier]

>   emacs -Q
>   Paste to *scratch* this code:

>       (defcustom my-dir nil
>           "doc"
>          :type 'directory)

>   Eval it.
>   M-x customize-option RET my-dir RET

Problem here: nil is not a directory, so the above defcustom is not
valid.  Oddly enough Customize does not signal the error, and instead
gets into a weird state.  Once you set my-dir to a string, things work
much better.


        Stefan