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.

Git/Hook.hs

@@ -28,7 +28,7 @@ instance Eq Hook where
 	a == b = hookName a == hookName b
 
 hookFile :: Hook -> Repo -> FilePath
-hookFile h r = localGitDir r </> "hooks" </> hookName h
+hookFile h r = fromRawFilePath (localGitDir r) </> "hooks" </> hookName h
 
 {- Writes a hook. Returns False if the hook already exists with a different
  - content. Upgrades old scripts.