Stop generating invalid doctree if "use_latex_toc" setting is True.
The "use_latex_toc" setting tells Docutils to leave the ToC generation
LaTeX (to get a ToC with page numbers).
The "contents" directive generates a `<topic>` node with a nested
`<pending>` node. By default, the `parts.Contents` transform replaces
the `<pending>` node with a generated ToC in a `<bullet_list>`.
Keep the `<pending>` node if "use_latex_toc" is True to avoid an
empty (and hence invalid) `<topic>`.
Change the LaTeX writer to extract the value of the "content"
directive's options from the `<pending>` node.
This allows to drop "local" and "depth" from the attribute list of
`<topic>`, the "attributes reference" section in doctree.txt, and
the valid attributes in nodes.py.
git-svn-id: http://svn.code.sf.net/p/docutils/code/trunk@9719 929543f6-e4f2-0310-98a6-ba3bd3dd1d04