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.

Command/Fsck.hs

@@ -313,7 +313,7 @@ verifyRequiredContent _ _ = return True
 verifyAssociatedFiles :: Key -> KeyStatus -> RawFilePath -> Annex Bool
 verifyAssociatedFiles key keystatus file = do
 	when (isKeyUnlockedThin keystatus) $ do
-		f <- inRepo $ toTopFilePath $ fromRawFilePath file
+		f <- inRepo $ toTopFilePath file
 		afs <- Database.Keys.getAssociatedFiles key
 		unless (getTopFilePath f `elem` map getTopFilePath afs) $
 			Database.Keys.addAssociatedFile key f