optimisation: stream keys through git cat-file --buffer

This is only implemented for git-annex get so far. It makes git-annex
get nearly twice as fast in a repo with 10k files, all of them present!

But, see the TODO for some caveats.

Command/Export.hs

@@ -200,7 +200,7 @@ changeExport r db (PreferredFiltered new) = do
 	mapdiff a oldtreesha newtreesha = do
 		(diff, cleanup) <- inRepo $
 			Git.DiffTree.diffTreeRecursive oldtreesha newtreesha
-		seekActions $ pure $ map a diff
+		sequence_ $ map a diff
 		void $ liftIO cleanup
 
 -- Map of old and new filenames for each changed ExportKey in a diff.

Command/Get.hs

@@ -40,12 +40,13 @@ optParser desc = GetOptions
 seek :: GetOptions -> CommandSeek
 seek o = startConcurrency downloadStages $ do
 	from <- maybe (pure Nothing) (Just <$$> getParsed) (getFrom o)
-	let go = whenAnnexed $ start o from
+	let go = start o from
 	case batchOption o of
-		Batch fmt -> batchFilesMatching fmt (go . toRawFilePath)
+		Batch fmt -> batchFilesMatching fmt
+			(whenAnnexed go . toRawFilePath)
 		NoBatch -> withKeyOptions (keyOptions o) (autoMode o)
 			(commandAction . startKeys from)
-			(withFilesInGit ww (commandAction . go))
+			(withFilesInGitAnnex ww (\f k -> commandAction (go f k)))
 			=<< workTreeItems ww (getFiles o)
   where
 	ww = WarnUnmatchLsFiles

Command/Multicast.hs

@@ -130,7 +130,7 @@ send ups fs = do
 	starting "sending files" (ActionItemOther Nothing) $
 		withTmpFile "send" $ \t h -> do
 			let ww = WarnUnmatchLsFiles
-			fs' <- seekHelper ww LsFiles.inRepo
+			fs' <- seekHelper id ww LsFiles.inRepo
 				=<< workTreeItems ww fs
 			matcher <- Limit.getMatcher
 			let addlist f o = whenM (matcher $ MatchingFile $ FileInfo f f) $

Command/Sync.hs

@@ -652,11 +652,11 @@ seekSyncContent o rs currbranch = do
 	liftIO $ not <$> isEmptyMVar mvar
   where
 	seekworktree mvar l bloomfeeder = 
-		seekHelper ww LsFiles.inRepo l
+		seekHelper id ww LsFiles.inRepo l
 			>>= gofiles bloomfeeder mvar
 
 	seekincludinghidden origbranch mvar l bloomfeeder = 
-		seekHelper ww (LsFiles.inRepoOrBranch origbranch) l 
+		seekHelper id ww (LsFiles.inRepoOrBranch origbranch) l 
 			>>= gofiles bloomfeeder mvar
 
 	ww = WarnUnmatchLsFiles