MIME: In looking up extensions, drop the encoding info.

E.g. for 'image/jpg;base64' we should lookup 'image/jpg'.

src/Text/Pandoc/MIME.hs

@@ -40,7 +40,8 @@ getMimeType f = M.lookup (map toLower $ drop 1 $ takeExtension f) mimeTypes
   where mimeTypes = M.fromList mimeTypesList
 
 extensionFromMimeType :: String -> Maybe String
-extensionFromMimeType mimetype = M.lookup mimetype reverseMimeTypes
+extensionFromMimeType mimetype = M.lookup (takeWhile (/=';') mimetype) reverseMimeTypes
+  -- note:  we just look up the basic mime type, dropping the content-encoding etc.
   where reverseMimeTypes = M.fromList $ map (\(k,v) -> (v,k)) mimeTypesList
 
 mimeTypesList :: [(String, String)]