Sped up query commands that read the git-annex branch by around 5%

The only price paid is one additional MVar read per write to the journal.
Presumably writing a journal file dominiates over a MVar read time by
several orders of magnitude.

--batch does not get the speedup because then it needs to notice when
another process has made a change. Also made the assistant and other damon
modes bypass the optimisation, which would not help them anyway.

Command/Forget.hs

@@ -45,7 +45,7 @@ perform :: Transitions -> Bool -> CommandPerform
 perform ts True = do
 	recordTransitions Branch.change ts
 	-- get branch committed before contining with the transition
-	Branch.update
+	_ <- Branch.update
 	void $ Branch.performTransitions ts True []
 	next $ return True
 perform _ False = do

Command/Merge.hs

@@ -30,7 +30,7 @@ seek bs = do
 
 mergeAnnexBranch :: CommandStart
 mergeAnnexBranch = starting "merge" (ActionItemOther (Just "git-annex")) $ do
-	Annex.Branch.update
+	_ <- Annex.Branch.update
 	-- commit explicitly, in case no remote branches were merged
 	Annex.Branch.commit =<< Annex.Branch.commitMessage
 	next $ return True

Command/TransferKeys.hs

@@ -17,6 +17,7 @@ import qualified Remote
 import Utility.SimpleProtocol (dupIoHandles)
 import Git.Types (RemoteName)
 import qualified Database.Keys
+import Annex.BranchState
 
 data TransferRequest = TransferRequest Direction Remote Key AssociatedFile
 
@@ -29,6 +30,7 @@ seek = withNothing (commandAction start)
 
 start :: CommandStart
 start = do
+	enableInteractiveJournalAccess
 	(readh, writeh) <- liftIO dupIoHandles
 	runRequests readh writeh runner
 	stop