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/Unused.hs

@@ -64,7 +64,7 @@ describeUnused' whenbig = liftAnnex $ go =<< readUnusedLog ""
 
 	sumkeysize s k = s + fromMaybe 0 (fromKey keySize k)
 
-	forpath a = inRepo $ liftIO . a . Git.repoPath
+	forpath a = inRepo $ liftIO . a . fromRawFilePath . Git.repoPath
 
 {- With a duration, expires all unused files that are older.
  - With Nothing, expires *all* unused files. -}