Don't wrap headers in markdown or rst.

src/Text/Pandoc/Writers/Markdown.hs

@@ -234,7 +234,8 @@ blockToMarkdown opts (Header level inlines) = do
   contents <- inlineListToMarkdown opts inlines
   st <- get
   let setext = writerSetextHeaders opts
-  return $ case level of
+  return $ nowrap
+         $ case level of
             1 | setext ->
                   contents <> cr <> text (replicate (offset contents) '=') <>
                   blankline

src/Text/Pandoc/Writers/RST.hs

@@ -157,7 +157,7 @@ blockToRST (Header level inlines) = do
   contents <- inlineListToRST inlines
   let headerChar = if level > 5 then ' ' else "=-~^'" !! (level - 1)
   let border = text $ replicate (offset contents) headerChar
-  return $ contents $$ border $$ blankline
+  return $ nowrap $ contents $$ border $$ blankline
 blockToRST (CodeBlock (_,classes,_) str) = do
   opts <- stOptions <$> get
   let tabstop = writerTabStop opts