'Get the number of duplicate refs of the footnote.'

def get_num_duplicates(self, li):

    (fn, rest) = li.attrib.get(u'id', u'').split(self.footnotes.get_separator(), 1)
    link_id = (u'%sref%s%s' % (fn, self.footnotes.get_separator(), rest))
    return self.footnotes.found_refs.get(link_id, 0)
