emacs-wiki-link-url: return relative links

(defadvice emacs-wiki-link-url (around sacha activate)
  "Return relative links if possible."
  ad-do-it
  (when ad-return-value
    (unless (emacs-wiki-wiki-url-p ad-return-value)
      (setq ad-return-value
            (file-relative-name
             ad-return-value
             (if (string-match "public_html" ad-return-value)
                 "../../public_html/notebook/plans"
               "../../notebook/plans")))
      (when (and sacha/emacs-wiki-use-absolute-url-flag
                 emacs-wiki-publishing-p)
        (setq ad-return-value
              (w3m-expand-url
               ad-return-value
               "http://sacha.free.net.ph/notebook/wiki/"))))))