This is needed so that SVG files are included as an <object...> rather
than as an <img...>, which in turn is needed to ensure SVG tooltips
will work. We do not explicitly require org-mode 9.1, but we install
it if it is not present.
* HACKING: Mention the requirement.
* doc/org/.dir-locals.el.in, doc/org/init.el.in, doc/org/spot.css:
Adjust to org-mode 9.1.
* doc/Makefile.am: Run emacs with the site-lisp libraries, in
case it contains a more recent org-mode.
* elisp/ob-dot.el: Delete, this was a work around older versions.
* elisp/Makefile.am: Adjust.