def activable_li_tag(*url, &block)
      content_tag :li, capture(&block), :class => ("active" if url.any?{|u| current_page?(u)})
    end
def activable_li_tag(*url, &block)
      content_tag :li, capture(&block), :class => ("active" if url.any?{|u| current_page?(u)})
    end
+li+ tag with the 'active' class added if the url is the current one.
 Eg.:

   <%= activable_li_tag users_path do  %>
     <%= link_to "Users", users_path %>
   <% end %>