arrange for regional output manager to run when -J is enabled

Commands that want to use it have to run their seek action inside
allowConcurrentOutput. Which seems reasonable; perhaps some future command
will want to support the -J flag but not use regions.

The region state moved from Annex to MessageState. This makes sense
organizationally, and note that some uses of onLocal use a different Annex
state, but pass the MessageState into it, which is what is needed.

CmdLine/GitAnnex/Options.hs

@@ -282,13 +282,17 @@ jsonOption = globalFlag (Annex.setOutput JSONOutput)
 	<> hidden
 	)
 
+-- Note that a command that adds this option should wrap its seek
+-- action in `allowConcurrentOutput`.
 jobsOption :: GlobalOption
-jobsOption = globalSetter (Annex.setOutput . ConcurrentOutput) $ 
+jobsOption = globalSetter set $ 
 	option auto
 		( long "jobs" <> short 'J' <> metavar paramNumber
 		<> help "enable concurrent jobs"
 		<> hidden
 		)
+  where
+	set n = Annex.changeState $ \s -> s { Annex.concurrentjobs = Just n }
 
 timeLimitOption :: GlobalOption
 timeLimitOption = globalSetter Limit.addTimeLimit $ strOption