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.

Remote/Git.hs

@@ -6,6 +6,7 @@
  -}
 
 {-# LANGUAGE CPP #-}
+{-# LANGUAGE OverloadedStrings #-}
 
 module Remote.Git (
 	remote,
@@ -68,6 +69,7 @@ import Utility.FileMode
 import Control.Concurrent
 import Control.Concurrent.MSampleVar
 import qualified Data.Map as M
+import qualified Data.ByteString as S
 import Network.URI
 
 remote :: RemoteType
@@ -86,14 +88,14 @@ list autoinit = do
 	rs <- mapM (tweakurl c) =<< Annex.getGitRemotes
 	mapM (configRead autoinit) rs
   where
-	annexurl n = "remote." ++ n ++ ".annexurl"
+	annexurl n = "remote." <> encodeBS' n <> ".annexurl"
 	tweakurl c r = do
 		let n = fromJust $ Git.remoteName r
 		case M.lookup (annexurl n) c of
 			Nothing -> return r
 			Just url -> inRepo $ \g ->
 				Git.Construct.remoteNamed n $
-					Git.Construct.fromRemoteLocation url g
+					Git.Construct.fromRemoteLocation (decodeBS' url) g
 
 {- Git remotes are normally set up using standard git command, not
  - git-annex initremote and enableremote.
@@ -254,7 +256,7 @@ tryGitConfigRead autoinit r
 		v <- liftIO $ Git.Config.fromPipe r cmd params
 		case v of
 			Right (r', val) -> do
-				unless (isUUIDConfigured r' || null val) $ do
+				unless (isUUIDConfigured r' || S.null val) $ do
 					warning $ "Failed to get annex.uuid configuration of repository " ++ Git.repoDescribe r
 					warning $ "Instead, got: " ++ show val
 					warning $ "This is unexpected; please check the network transport!"