disentangle concurrency and message type

This makes -Jn work with --json and --quiet, where before
setting -Jn disabled those options.

Concurrent json output is currently a mess though since threads output
chunks over top of one-another.

Command/MetaData.hs

@@ -78,7 +78,7 @@ seek o = do
 				(startKeys now o)
 				(seeker $ whenAnnexed $ start now o)
 				(forFiles o)
-		Batch -> withOutputType $ \ot -> case ot of
+		Batch -> withMessageState $ \s -> case outputType s of
 			JSONOutput -> batchInput parseJSONInput $
 				commandAction . startBatch now
 			_ -> error "--batch is currently only supported in --json mode"