Fix for unquoted attribute values in mediawiki tables.

Previously an unquoted attribute value in a table row
could cause parsing problems.

Fixes #3053 (well, proper rowspans and colspans aren't
created, but that's a bigger limitation with the current
Pandoc document model for tables).

src/Text/Pandoc/Readers/MediaWiki.hs

@@ -253,7 +253,7 @@ parseAttr = try $ do
   k <- many1 letter
   char '='
   v <- (char '"' >> many1Till (satisfy (/='\n')) (char '"'))
-       <|> many1 nonspaceChar
+       <|> many1 (satisfy $ \c -> not (isSpace c) && c /= '|')
   return (k,v)
 
 tableStart :: MWParser ()