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.

Command/Find.hs

@@ -93,8 +93,8 @@ keyVars key =
 	, ("bytesize", size show)
 	, ("humansize", size $ roughSize storageUnits True)
 	, ("keyname", decodeBS $ fromKey keyName key)
-	, ("hashdirlower", hashDirLower def key)
-	, ("hashdirmixed", hashDirMixed def key)
+	, ("hashdirlower", fromRawFilePath $ hashDirLower def key)
+	, ("hashdirmixed", fromRawFilePath $ hashDirMixed def key)
 	, ("mtime", whenavail show $ fromKey keyMtime key)
 	]
   where