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/Git.hs

@@ -680,8 +680,8 @@ fsckOnRemote r params
 		r' <- Git.Config.read r
 		environ <- getEnvironment
 		let environ' = addEntries 
-			[ ("GIT_WORK_TREE", Git.repoPath r')
-			, ("GIT_DIR", Git.localGitDir r')
+			[ ("GIT_WORK_TREE", fromRawFilePath $ Git.repoPath r')
+			, ("GIT_DIR", fromRawFilePath $ Git.localGitDir r')
 			] environ
 		batchCommandEnv program (Param "fsck" : params) (Just environ')