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.

Command/Sync.hs

@@ -93,7 +93,7 @@ optParser desc = SyncOptions
 	<*> optional parseAllOption
 
 seek :: SyncOptions -> CommandSeek
-seek o = do
+seek o = allowConcurrentOutput $ do
 	prepMerge
 
 	-- There may not be a branch checked out until after the commit,