Refine check for denote dir in dired revert

This pertains to the post-rename operation where relevant Dired buffers
are reverted.  The previous check would sometimes compare incompatible
file paths and thus return nil when it shouldn't.

Thanks to Sven Seebeck for reporting the problem in issue 17 over at the
GitHub mirror: <https://github.com/protesilaos/denote/issues/17>.

denote-dired.el

@@ -261,7 +261,8 @@ ignores all its arguments."
    (lambda (buf)
      (with-current-buffer buf
        (when (and (eq major-mode 'dired-mode)
-                  (string-match-p (expand-file-name default-directory) (denote-directory)))
+                  (string-match-p (expand-file-name default-directory)
+                                  (expand-file-name (denote-directory))))
          (revert-buffer))))
    (buffer-list)))