finish CommandStart transition

The hoped for optimisation of CommandStart with -J did not materialize.
In fact, not runnign CommandStart in parallel is slower than -J3.
So, CommandStart are still run in parallel.

(The actual bad performance I've been seeing with -J in my big repo
has to do with building the remoteList.)

But, this is still progress toward making -J faster, because it gets rid
of the onlyActionOn roadblock in the way of making CommandCleanup jobs
run separate from CommandPerform jobs.

Added OnlyActionOn constructor for ActionItem which fixes the
onlyActionOn breakage in the last commit.

Made CustomOutput include an ActionItem, so even things using it can
specify OnlyActionOn.

In Command.Move and Command.Sync, there were CommandStarts that used
includeCommandAction, so output messages, which is no longer allowed.
Fixed by using startingCustomOutput, but that's still not quite right,
since it prevents message display for the includeCommandAction run
inside it too.

Command/Move.hs

@@ -108,8 +108,9 @@ toStart' dest removewhen afile key ai = do
 			)
 		else go False (Remote.hasKey dest key)
   where
-	go fastcheck isthere = starting (describeMoveAction removewhen) ai $
-		toPerform dest removewhen key afile fastcheck =<< isthere
+	go fastcheck isthere =
+		starting (describeMoveAction removewhen) (OnlyActionOn key ai) $
+			toPerform dest removewhen key afile fastcheck =<< isthere
 
 expectedPresent :: Remote -> Key -> Annex Bool
 expectedPresent dest key = do
@@ -182,7 +183,7 @@ fromStart removewhen afile key ai src = case removewhen of
 	RemoveSafe -> go
   where
 	go = stopUnless (fromOk src key) $
-		starting (describeMoveAction removewhen) ai $
+		starting (describeMoveAction removewhen) (OnlyActionOn key ai) $
 			fromPerform src removewhen key afile
 
 fromOk :: Remote -> Key -> Annex Bool
@@ -246,13 +247,13 @@ toHereStart removewhen afile key ai = case removewhen of
 	RemoveNever -> stopUnless (not <$> inAnnex key) go
 	RemoveSafe -> go
   where
-	go = do
+	go = startingCustomOutput (OnlyActionOn key ai) $ do
 		rs <- Remote.keyPossibilities key
 		forM_ rs $ \r ->
 			includeCommandAction $
 				starting (describeMoveAction removewhen) ai $
 					fromPerform r removewhen key afile
-		stop
+		next $ return True
 
 {- The goal of this command is to allow the user maximum freedom to move
  - files as they like, while avoiding making bad situations any worse