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.

Upgrade.hs

@@ -48,7 +48,7 @@ needsUpgrade v
   where
 	err msg = do
 		g <- Annex.gitRepo
-		p <- liftIO $ absPath $ Git.repoPath g
+		p <- liftIO $ absPath $ fromRawFilePath $ Git.repoPath g
 		return $ Just $ unwords
 			[ "Repository", p
 			, "is at unsupported version"