bug#6539: ispell-complete-word looks for wrong file (at least on w32)

[Eli Zaretskii]

> From: Lennart Borgman <lennart.borgman@gmail.com>
> Date: Wed, 30 Jun 2010 13:45:56 +0200
> Cc: 6539@debbugs.gnu.org
> 
> OK, thanks. The default for ispell-alternate-dictionary is not a full
> path on w32 so that is a bug.

How would you suggest to fix this "bug"?  I see only 2 possibilities
(besides leaving this as they are and letting w32 users customize the
value, as I did): either (a) signal an error, or (b) search the entire
hard disk storage for a file named `words'.