use ByteString for git config

The parser and looking up config keys in the map should both be faster
due to using ByteString.

I had hoped this would speed up startup time, but any improvement to
that was too small to measure. Seems worth keeping though.

Note that the parser breaks up the ByteString, but a config map ends up
pointing to the config as read, which is retained in memory until every
value from it is no longer used. This can change memory usage
patterns marginally, but won't affect git-annex.

Git/Remote.hs

@@ -6,6 +6,7 @@
  -}
 
 {-# LANGUAGE CPP #-}
+{-# LANGUAGE OverloadedStrings #-}
 
 module Git.Remote where
 
@@ -15,18 +16,20 @@ import Git.Types
 
 import Data.Char
 import qualified Data.Map as M
+import qualified Data.ByteString as S
+import qualified Data.ByteString.Char8 as S8
 import Network.URI
 #ifdef mingw32_HOST_OS
 import Git.FilePath
 #endif
 
 {- Is a git config key one that specifies the location of a remote? -}
-isRemoteKey :: String -> Bool
-isRemoteKey k = "remote." `isPrefixOf` k && ".url" `isSuffixOf` k
+isRemoteKey :: S.ByteString -> Bool
+isRemoteKey k = "remote." `S.isPrefixOf` k && ".url" `S.isSuffixOf` k
 
 {- Get a remote's name from the config key that specifies its location. -}
-remoteKeyToRemoteName :: String -> RemoteName
-remoteKeyToRemoteName k = intercalate "." $ dropFromEnd 1 $ drop 1 $ splitc '.' k
+remoteKeyToRemoteName :: S.ByteString -> RemoteName
+remoteKeyToRemoteName = decodeBS' . S.intercalate "." . dropFromEnd 1 . drop 1 . S8.split '.'
 
 {- Construct a legal git remote name out of an arbitrary input string.
  -
@@ -76,16 +79,16 @@ parseRemoteLocation s repo = ret $ calcloc s
 	-- insteadof config can rewrite remote location
 	calcloc l
 		| null insteadofs = l
-		| otherwise = replacement ++ drop (length bestvalue) l
+		| otherwise = replacement ++ drop (S.length bestvalue) l
 	  where
-		replacement = drop (length prefix) $
-			take (length bestkey - length suffix) bestkey
+		replacement = decodeBS' $ S.drop (S.length prefix) $
+			S.take (S.length bestkey - S.length suffix) bestkey
 		(bestkey, bestvalue) = maximumBy longestvalue insteadofs
 		longestvalue (_, a) (_, b) = compare b a
 		insteadofs = filterconfig $ \(k, v) -> 
-			prefix `isPrefixOf` k &&
-			suffix `isSuffixOf` k &&
-			v `isPrefixOf` l
+			prefix `S.isPrefixOf` k &&
+			suffix `S.isSuffixOf` k &&
+			v `S.isPrefixOf` encodeBS l
 		filterconfig f = filter f $
 			concatMap splitconfigs $ M.toList $ fullconfig repo
 		splitconfigs (k, vs) = map (\v -> (k, v)) vs