HTML Reader: Recognise <br> tags inside <pre> blocks

Closes #1620

src/Text/Pandoc/Readers/HTML.hs

@@ -440,7 +440,7 @@ pCodeBlock :: TagParser Blocks
 pCodeBlock = try $ do
   TagOpen _ attr <- pSatisfy (~== TagOpen "pre" [])
   contents <- manyTill pAnyTag (pCloses "pre" <|> eof)
-  let rawText = concatMap fromTagText $ filter isTagText contents
+  let rawText = concatMap tagToString contents
   -- drop leading newline if any
   let result' = case rawText of
                      '\n':xs  -> xs
@@ -451,6 +451,11 @@ pCodeBlock = try $ do
                     _        -> result'
   return $ B.codeBlockWith (mkAttr attr) result
 
+tagToString :: Tag String -> String
+tagToString (TagText s) = s
+tagToString (TagOpen "br" _) = "\n"
+tagToString _ = ""
+
 inline :: TagParser Inlines
 inline = choice
            [ eNoteref