Sped up unused.

Added Git.ByteString which replaces Git IO methods with ones using lazy
ByteStrings. This can be more efficient when large quantities of data are
being read from git.

In Git.LsTree, parse git ls-tree output more efficiently, thanks
to ByteString. This benchmarks 25% faster, in a benchmark that includes
(probably predominately) the run time for git ls-tree itself.

In real world numbers, this makes git annex unused 2 seconds faster for
each branch it needs to check, in my usual large repo.

Git/LsTree.hs

@@ -7,22 +7,23 @@
 
 module Git.LsTree (
 	TreeItem(..),
-	lsTree
+	lsTree,
+	parseLsTree
 ) where
 
 import Numeric
 import Control.Applicative
-import Data.Char
 import System.Posix.Types
+import qualified Data.ByteString.Lazy.Char8 as L
 
-import Git
+import Git.ByteString
 import Utility.SafeCommand
 
 type Treeish = String
 
 data TreeItem = TreeItem
 	{ mode :: FileMode
-	, objtype :: String
+	, typeobj :: String
 	, sha :: String
 	, file :: FilePath
 	} deriving Show
@@ -34,18 +35,17 @@ lsTree repo t = map parseLsTree <$>
 
 {- Parses a line of ls-tree output.
  - (The --long format is not currently supported.) -}
-parseLsTree :: String -> TreeItem
-parseLsTree l = TreeItem m o s f
+parseLsTree :: L.ByteString -> TreeItem
+parseLsTree l = TreeItem
+		(fst $ head $ readOct $ L.unpack m)
+		(L.unpack t)
+		(L.unpack s)
+		(decodeGitFile $ L.unpack f)
 	where
 		-- l = <mode> SP <type> SP <sha> TAB <file>
-		-- Since everything until the file is fixed-width,
-		-- do not need to split on words.
-		(m, past_m) = head $ readOct l
-		(o, past_o) = splitAt 4 $ space past_m
-		(s, past_s) = splitAt shaSize $ space past_o
-		f = decodeGitFile $ space past_s
-		space (sp:rest)
-			| isSpace sp = rest
-			| otherwise = parseerr
-		space [] = parseerr
-		parseerr = "ls-tree parse error: " ++ l
+		-- All fields are fixed, so we can pull them out of
+		-- specific positions in the line.
+		(m, past_m) = L.splitAt 7 l
+		(t, past_t) = L.splitAt 4 past_m
+		(s, past_s) = L.splitAt 40 $ L.tail past_t
+		f = L.tail past_s