Markdown reader: fenced div takes priority over setext header.

For

    ::: {.cell}
    ---
    :::

src/Text/Pandoc/Readers/Markdown.hs

@@ -489,10 +489,10 @@ block = do
                -- note: bulletList needs to be before header because of
                -- the possibility of empty list items: -
                , bulletList
-               , header
-               , lhsCodeBlock
                , divHtml
                , divFenced
+               , header
+               , lhsCodeBlock
                , htmlBlock
                , table
                , codeBlockIndented

test/command/setext-fenced-div.md

@@ -0,0 +1,9 @@
+```
+% pandoc -t native
+::: {.cell}
+---
+:::
+^D
+[Div ("",["cell"],[])
+ [HorizontalRule]]
+```