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/GCrypt.hs

@@ -7,6 +7,8 @@
  - Licensed under the GNU AGPL version 3 or higher.
  -}
 
+{-# LANGUAGE OverloadedStrings #-}
+
 module Git.GCrypt where
 
 import Common
@@ -16,6 +18,8 @@ import qualified Git.Config as Config
 import qualified Git.Command as Command
 import Utility.Gpg
 
+import qualified Data.ByteString as S
+
 urlScheme :: String
 urlScheme = "gcrypt:"
 
@@ -75,9 +79,9 @@ type GCryptId = String
  - which is stored in the repository (in encrypted form)
  - and cached in a per-remote gcrypt-id configuration setting. -}
 remoteRepoId :: Repo -> Maybe RemoteName -> Maybe GCryptId
-remoteRepoId = getRemoteConfig "gcrypt-id"
+remoteRepoId r n = decodeBS' <$> getRemoteConfig "gcrypt-id" r n
 
-getRemoteConfig :: String -> Repo -> Maybe RemoteName -> Maybe String
+getRemoteConfig :: S.ByteString -> Repo -> Maybe RemoteName -> Maybe S.ByteString
 getRemoteConfig field repo remotename = do
 	n <- remotename
 	Config.getMaybe (remoteConfigKey field n) repo
@@ -93,17 +97,17 @@ getParticiantList globalconfigrepo repo remotename = KeyIds $ parse $ firstJust
   where
 	defaultkey = "gcrypt.participants"
 	parse (Just "simple") = []
-	parse (Just l) = words l
+	parse (Just b) = words (decodeBS' b)
 	parse Nothing = []
 
-remoteParticipantConfigKey :: RemoteName -> String
+remoteParticipantConfigKey :: RemoteName -> S.ByteString
 remoteParticipantConfigKey = remoteConfigKey "gcrypt-participants"
 
-remotePublishParticipantConfigKey :: RemoteName -> String
+remotePublishParticipantConfigKey :: RemoteName -> S.ByteString
 remotePublishParticipantConfigKey = remoteConfigKey "gcrypt-publish-participants"
 
-remoteSigningKey :: RemoteName -> String
+remoteSigningKey :: RemoteName -> S.ByteString
 remoteSigningKey = remoteConfigKey "gcrypt-signingkey"
 
-remoteConfigKey :: String -> RemoteName -> String
-remoteConfigKey key remotename = "remote." ++ remotename ++ "." ++ key
+remoteConfigKey :: S.ByteString -> RemoteName -> S.ByteString
+remoteConfigKey key remotename = "remote." <> encodeBS' remotename <> "." <> key