find-alternate-file broken in files.el 1.633

[Bob Halley]

When I try to use find-alternate-file in the latest CVS (files.el
1.633) I get an error:

call-interactively: Symbol's value as variable is void: dired-directory

This change in 1.633 appears to be the culprit:

   (let ((obuf (current-buffer))
        (ofile buffer-file-name)
        (onum buffer-file-number)
+       (odir dired-directory)
        (otrue buffer-file-truename)
        (oname (buffer-name)))
     (if (get-buffer " **lose**")

I'm not sure how to fix this, since I know little about
dired-directory.  In particular, I don't know if we should just check
if it is bound and set odir to nil if it isn't, or if it is in fact an
error that dired-directory isn't bound and we should fix that instead.

/Bob