convert TopFilePath to use RawFilePath

Adds a dependency on filepath-bytestring, an as yet unreleased fork of
filepath that operates on RawFilePath.

Git.Repo also changed to use RawFilePath for the path to the repo.

This does eliminate some RawFilePath -> FilePath -> RawFilePath
conversions. And filepath-bytestring's </> is probably faster.
But I don't expect a major performance improvement from this.
This is mostly groundwork for making Annex.Location use RawFilePath,
which will allow for a conversion-free pipleline.

Assistant/WebApp/Configurators/Pairing.hs

@@ -173,7 +173,7 @@ getFinishLocalPairR = postFinishLocalPairR
 postFinishLocalPairR :: PairMsg -> Handler Html
 #ifdef WITH_PAIRING
 postFinishLocalPairR msg = promptSecret (Just msg) $ \_ secret -> do
-	repodir <- liftH $ repoPath <$> liftAnnex gitRepo
+	repodir <- liftH $ fromRawFilePath . repoPath <$> liftAnnex gitRepo
 	liftIO $ setup repodir
 	startLocalPairing PairAck (cleanup repodir) alert uuid "" secret
   where