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/Helper/Ssh.hs

@@ -65,7 +65,7 @@ git_annex_shell cs r command params fields
 		let params' = if debug
 			then Param "--debug" : params
 			else params
-		return (Param command : File dir : params')
+		return (Param command : File (fromRawFilePath dir) : params')
 	uuidcheck NoUUID = []
 	uuidcheck u@(UUID _) = ["--uuid", fromUUID u]
 	fieldopts