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.

Command/ReKey.hs

@@ -123,7 +123,7 @@ cleanup file oldkey newkey = do
 				writePointerFile file newkey mode
 			stagePointerFile file mode =<< hashPointerFile newkey
 			Database.Keys.removeAssociatedFile oldkey 
-				=<< inRepo (toTopFilePath (fromRawFilePath file))
+				=<< inRepo (toTopFilePath file)
 		)
 	whenM (inAnnex newkey) $
 		logStatus newkey InfoPresent