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.