use filepath-bytestring for annex object manipulations

git-annex find is now RawFilePath end to end, no string conversions.
So is git-annex get when it does not need to get anything.
So this is a major milestone on optimisation.

Benchmarks indicate around 30% speedup in both commands.

Probably many other performance improvements. All or nearly all places
where a file is statted use RawFilePath now.

Assistant/Upgrade.hs

@@ -113,7 +113,7 @@ distributionDownloadComplete d dest cleanup t
 	| transferDirection t == Download = do
 		debug ["finished downloading git-annex distribution"]
 		maybe (failedupgrade "bad download") go
-			=<< liftAnnex (withObjectLoc k fsckit)
+			=<< liftAnnex (withObjectLoc k (fsckit . fromRawFilePath))
 	| otherwise = cleanup
   where
 	k = mkKey $ const $ distributionKey d