rewrite loggedkeys to use git-annex branch

That sucking sound is a whole page of code vanishing to be replaced with
  return . catMaybes . map (logFileKey . takeFileName) =<< Branch.files
What can I say, git is my database, and haskell my copilot.

Branch.hs

@@ -11,7 +11,7 @@ module Branch (
 	get,
 	change,
 	commit,
-	shortref
+	files
 ) where
 
 import Control.Monad (unless, when, liftM)
@@ -222,3 +222,10 @@ cmdOutput cmd params = do
 	let rv = seq retval retval
 	_ <- getProcessStatus True False pid
 	return rv
+
+{- Lists all files on the branch. -}
+files :: Annex [FilePath]
+files = withIndexUpdate $ do
+	g <- Annex.gitRepo
+	liftIO $ Git.pipeNullSplit g
+		[Params "ls-tree --name-only -r -z", Param fullname]

Command/Unused.hs

@@ -66,10 +66,8 @@ checkRemoteUnused name = do
 checkRemoteUnused' :: Remote.Remote Annex -> Annex ()
 checkRemoteUnused' r = do
 	showNote $ "checking for unused data..."
-	g <- Annex.gitRepo
 	referenced <- getKeysReferenced
-	logged <- loggedKeys g
-	remotehas <- filterM isthere logged
+	remotehas <- filterM isthere =<< loggedKeys
 	let remoteunused = remotehas `exclude` referenced
 	let list = number 0 remoteunused
 	writeUnusedFile "" list

LocationLog.hs

@@ -26,7 +26,6 @@ module LocationLog (
 import Data.Time.Clock.POSIX
 import Data.Time
 import System.Locale
-import System.Directory
 import System.FilePath
 import qualified Data.Map as Map
 import Control.Monad (when)
@@ -35,7 +34,6 @@ import Control.Monad.State (liftIO)
 
 import qualified GitRepo as Git
 import qualified Branch
-import Utility
 import UUID
 import Types
 import Locations
@@ -148,19 +146,6 @@ mapLog m l =
 
 {- Finds all keys that have location log information.
  - (There may be duplicate keys in the list.) -}
-loggedKeys :: Git.Repo -> Annex [Key]
-loggedKeys repo = do
-	_ <- error "FIXME.. does not look in git-annex branch yet"
-	exists <- liftIO $ doesDirectoryExist dir
-	if exists
-		then do
-			-- 2 levels of hashing
-			levela <- liftIO $ dirContents dir
-			levelb <- mapM tryDirContents levela
-			files <- mapM tryDirContents (concat levelb)
-			return $ catMaybes $
-				map (logFileKey . takeFileName) (concat files)
-		else return []
-	where
-		tryDirContents d = liftIO $ catch (dirContents d) (return . const [])
-		dir = gitStateDir repo
+loggedKeys :: Annex [Key]
+loggedKeys =
+	return . catMaybes . map (logFileKey . takeFileName) =<< Branch.files