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.

P2P/IO.hs

@@ -293,7 +293,7 @@ runRelayService conn runner service =
 	
 	serviceproc = gitCreateProcess
 		[ Param cmd
-		, File (repoPath (connRepo conn))
+		, File (fromRawFilePath (repoPath (connRepo conn)))
 		] (connRepo conn)
 
 	setup = do