Changed hierarchicalize so it treats references div as top-level header.

Fixes a bug with `--section-divs`, where the final references section
added by pandoc-citeproc, enclosed in its own div, got put in the
div for the section previous to it.

This fixes #2294.  Longer term, we might think about how hierarchicalize
should interact with Div elements.

src/Text/Pandoc/Shared.hs

@@ -662,12 +662,17 @@ hierarchicalizeWithIds ((Header level attr@(_,classes,_) title'):xs) = do
   sectionContents' <- hierarchicalizeWithIds sectionContents
   rest' <- hierarchicalizeWithIds rest
   return $ Sec level newnum attr title' sectionContents' : rest'
+hierarchicalizeWithIds ((Div ("",["references"],[])
+                         (Header level (ident,classes,kvs) title' : xs)):ys) =
+  hierarchicalizeWithIds ((Header level (ident,("references":classes),kvs)
+                           title') : (xs ++ ys))
 hierarchicalizeWithIds (x:rest) = do
   rest' <- hierarchicalizeWithIds rest
   return $ (Blk x) : rest'
 
 headerLtEq :: Int -> Block -> Bool
 headerLtEq level (Header l _ _) = l <= level
+headerLtEq level (Div ("",["references"],[]) (Header l _ _ : _))  = l <= level
 headerLtEq _ _ = False
 
 -- | Generate a unique identifier from a list of inlines.