Filter LIs in reverse

I'm almost certain what's happening is that as we filter each
XPath query result, modifications are invalidating other
elements needing to be updated within the same tree, for example
nested Task Lists. This is the most direct fix, but far from
the most elegant.

Author: mtodd

lib/task_list/filter.rb

@@ -113,7 +113,7 @@ def task_lists
     def filter_list(node)
       add_css_class(node, 'task-list')
 
-      node.xpath(ItemSelector).each do |li|
+      node.xpath(ItemSelector).reverse.each do |li|
         outer, inner =
           if p = li.xpath(ItemParaSelector)[0]
             [p, p.inner_html]
@@ -122,7 +122,8 @@ def filter_list(node)
           end
         if match = (inner.chomp =~ ItemPattern && $1)
           item = TaskList::Item.new(match, inner)
-          task_list_items << item
+          # prepend because we're iterating in reverse
+          task_list_items.unshift item
 
           add_css_class(li, 'task-list-item')
           outer.inner_html = render_task_list_item(item)