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.

Remote/Bup.hs

@@ -230,7 +230,7 @@ onBupRemote r runner command params = do
 	(sshcmd, sshparams) <- Ssh.toRepo NoConsumeStdin r c remotecmd
 	liftIO $ runner sshcmd sshparams
   where
-	path = Git.repoPath r
+	path = fromRawFilePath $ Git.repoPath r
 	base = fromMaybe path (stripPrefix "/~/" path)
 	dir = shellEscape base