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/Helper/Special.hs

@@ -5,6 +5,8 @@
  - Licensed under the GNU AGPL version 3 or higher.
  -}
 
+{-# LANGUAGE OverloadedStrings #-}
+
 module Remote.Helper.Special (
 	findSpecialRemotes,
 	gitConfigSpecialRemote,
@@ -52,6 +54,7 @@ import Messages.Progress
 import qualified Git
 import qualified Git.Construct
 
+import qualified Data.ByteString as S
 import qualified Data.ByteString.Lazy as L
 import qualified Data.Map as M
 
@@ -65,14 +68,15 @@ findSpecialRemotes s = do
 	liftIO $ mapM construct $ remotepairs m
   where
 	remotepairs = M.toList . M.filterWithKey match
-	construct (k,_) = Git.Construct.remoteNamedFromKey k (pure Git.Construct.fromUnknown)
-	match k _ = "remote." `isPrefixOf` k && (".annex-"++s) `isSuffixOf` k
+	construct (k,_) = Git.Construct.remoteNamedFromKey k
+		(pure Git.Construct.fromUnknown)
+	match k _ = "remote." `S.isPrefixOf` k && (".annex-" <> encodeBS' s) `S.isSuffixOf` k
 
 {- Sets up configuration for a special remote in .git/config. -}
 gitConfigSpecialRemote :: UUID -> RemoteConfig -> [(String, String)] -> Annex ()
 gitConfigSpecialRemote u c cfgs = do
 	forM_ cfgs $ \(k, v) -> 
-		setConfig (remoteConfig c k) v
+		setConfig (remoteConfig c (encodeBS' k)) v
 	storeUUIDIn (remoteConfig c "uuid") u
 
 -- RetrievalVerifiableKeysSecure unless overridden by git config.