org-odt.el: Render links to outline headings as section nos

org-odt.el: Render links to outline headings as section nos

* lisp/org-lparse.el (org-do-lparse): Make effective setting
of `org-export-headline-levels' available to the ODT exporter.
Also remove some stale comments.

* lisp/org-odt.el (org-odt-format-link): Add support for
generating cross-references to chapter numbers.
(org-odt-format-org-link): Resolve links to outline headings
as section numbers.  This special case resolution kicks in
only if the Org link has no description and the target outline
is not listified i.e., it is at a level within
`org-export-headline-levels'.

Fix for the following request:
http://lists.gnu.org/archive/html/emacs-orgmode/2012-02/msg01035.html

The above change is in conformity with the way links to
headlines will be treated in new ODT exporter that will be
built on top of Nicolas' org-element/org-export
infrastructure.