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/Types.hs

@@ -30,8 +30,8 @@ import Utility.FileSystemEncoding
  - else known about it.
  -}
 data RepoLocation
-	= Local { gitdir :: FilePath, worktree :: Maybe FilePath }
-	| LocalUnknown FilePath
+	= Local { gitdir :: RawFilePath, worktree :: Maybe RawFilePath }
+	| LocalUnknown RawFilePath
 	| Url URI
 	| Unknown
 	deriving (Show, Eq, Ord)