RawFilePath conversion of System.Directory

By using System.Directory.OsPath, which takes and returns OsString,
which is a ShortByteString. So, things like dirContents currently have the
overhead of copying that to a ByteString, but that should be less than
the overhead of using Strings which often in turn were converted to
RawFilePaths.

Added Utility.OsString and the OsString build flag. That flag is turned
on in the stack.yaml, and will be turned on automatically by cabal when
built with new enough libraries. The stack.yaml change is a bit ugly,
and that could be reverted for now if it causes any problems.

Note that Utility.OsString.toOsString on windows is avoiding only a
check of encoding that is documented as being unlikely to fail. I don't
think it can fail in git-annex; if it could, git-annex didn't contain
such an encoding check before, so at worst that should be a wash.

Assistant/Upgrade.hs

@@ -41,6 +41,7 @@ import qualified Utility.Url as Url
 import qualified Annex.Url as Url hiding (download)
 import Utility.Tuple
 import qualified Utility.RawFilePath as R
+import qualified System.FilePath.ByteString as P
 
 import Data.Either
 import qualified Data.Map as M
@@ -212,8 +213,8 @@ upgradeToDistribution newdir cleanup distributionfile = do
 			makeorigsymlink olddir
 		return (newdir </> "git-annex", deleteold)
 	installby a dstdir srcdir =
-		mapM_ (\x -> a (toRawFilePath x) (toRawFilePath (dstdir </> takeFileName x)))
-			=<< dirContents srcdir
+		mapM_ (\x -> a x (toRawFilePath dstdir P.</> P.takeFileName x))
+			=<< dirContents (toRawFilePath srcdir)
 #endif
 	sanitycheck dir = 
 		unlessM (doesDirectoryExist dir) $
@@ -280,14 +281,14 @@ deleteFromManifest dir = do
 	fs <- map (dir </>) . lines <$> catchDefaultIO "" (readFile manifest)
 	mapM_ (removeWhenExistsWith R.removeLink . toRawFilePath) fs
 	removeWhenExistsWith R.removeLink (toRawFilePath manifest)
-	removeEmptyRecursive dir
+	removeEmptyRecursive (toRawFilePath dir)
   where
 	manifest = dir </> "git-annex.MANIFEST"
 
-removeEmptyRecursive :: FilePath -> IO ()
+removeEmptyRecursive :: RawFilePath -> IO ()
 removeEmptyRecursive dir = do
 	mapM_ removeEmptyRecursive =<< dirContents dir
-	void $ tryIO $ removeDirectory dir
+	void $ tryIO $ removeDirectory (fromRawFilePath dir)
 
 {- This is a file that the UpgradeWatcher can watch for modifications to
  - detect when git-annex has been upgraded.