address some unused loop control variables

This is done by moving the sorting from the glossary directive to a
transform operating after the i18n transform.

Closes #9827

Node.traverse() was marked as deprecated since docutils-0.18.  Instead
of it, Node.findall() has been added as successor of traverse().

This applies a patch to docutils-0.17 or older to be available
Node.findall() and use it.

i18n feature for meta strings does not work if docutils-0.18 used.

Note: Since docutils-0.18, patch for meta directive is no longer
needed because it uses a picklable meta nodes; ``docutils.nodes.meta``.

It seems docutils does not fill the topic node with the source info when
a topic directive has a bullet list.  As a workaround, This fills the
source info of them.

The last fix in i18n module was incorrect because it compares the
"already consumed" generators.  It should compares the lists of nodes.

Since 0.18, Element.traverse() returns an iterator instead of
intermediate object.  As a result, the return value is always considered
as truthy value.  And it becomes fragile when the caller modifies the
doctree on the loop.