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.

Remote/GCrypt.hs

@@ -422,7 +422,8 @@ checkKey' repo r rsyncopts k
 {- Annexed objects are hashed using lower-case directories for max
  - portability. -}
 gCryptLocation :: Git.Repo -> Key -> FilePath
-gCryptLocation repo key = Git.repoLocation repo </> objectDir </> keyPath key (hashDirLower def)
+gCryptLocation repo key = Git.repoLocation repo </> objectDir
+	</> fromRawFilePath (keyPath key (hashDirLower def))
 
 data AccessMethod = AccessDirect | AccessShell