defer updating unlocked files until after smudge filter

The smuge filter no longer provides git with annexed file content, to
avoid a git memory leak, and because that did not honor annex.thin.

git annex smudge --update has to be run after a checkout to update
unlocked files in the working tree with annexed file contents.

No hooks yet to run it.

This commit was sponsored by Nick Piper on Patreon.

Logs/Smudge.hs

@@ -0,0 +1,40 @@
+{- git-annex smudge log file
+ -
+ - Copyright 2018 Joey Hess <id@joeyh.name>
+ -
+ - Licensed under the GNU AGPL version 3 or higher.
+ -}
+
+module Logs.Smudge where
+
+import Annex.Common
+import Git.FilePath
+import Logs.File
+
+-- | Log a smudged file.
+smudgeLog :: Key -> TopFilePath -> Annex ()
+smudgeLog k f = do
+	logf <- fromRepo gitAnnexSmudgeLog
+	appendLogFile logf gitAnnexSmudgeLock $ 
+		key2file k ++ " " ++ getTopFilePath f
+
+-- | Streams all smudged files, and then empties the log at the end.
+--
+-- If the action is interrupted or throws an exception, the log file is
+-- left unchanged.
+--
+-- Locking is used to prevent new items being added to the log while this
+-- is running.
+streamSmudged :: (Key -> TopFilePath -> Annex ()) -> Annex ()
+streamSmudged a = do
+	logf <- fromRepo gitAnnexSmudgeLog
+	streamLogFile logf gitAnnexSmudgeLock $ \l -> 
+		case parse l of
+			Nothing -> noop
+			Just (k, f) -> a k f
+  where
+	parse l = 
+		let (ks, f) = separate (== ' ') l
+		in do
+			k <- file2key ks
+			return (k, asTopFilePath f)