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/UnionMerge.hs

@@ -91,7 +91,7 @@ mergeFile info file hashhandle h = case filter (/= nullSha) [Ref asha, Ref bsha]
   where
 	[_colonmode, _bmode, asha, bsha, _status] = words info
 	use sha = return $ Just $
-		updateIndexLine sha TreeFile $ asTopFilePath file
+		updateIndexLine sha TreeFile $ asTopFilePath $ toRawFilePath file
 	-- Get file and split into lines to union merge.
 	-- The encoding of the file is assumed to be either ASCII or utf-8;
 	-- in either case it's safe to split on \n