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.

Utility/LockFile/PidLock.hs

@@ -39,6 +39,7 @@ import Utility.FileSystemEncoding
 import Utility.Env
 import Utility.Env.Set
 import Utility.Tmp
+import Utility.RawFilePath
 import qualified Utility.LockFile.Posix as Posix
 
 import System.IO
@@ -242,15 +243,14 @@ linkToLock (Just _) src dest = do
 -- with the SAME FILENAME exist.
 checkInsaneLustre :: RawFilePath -> IO Bool
 checkInsaneLustre dest = do
-	let dest' = fromRawFilePath dest
-	fs <- dirContents (takeDirectory dest')
-	case length (filter (== dest') fs) of
+	fs <- dirContents (P.takeDirectory dest)
+	case length (filter (== dest) fs) of
 		1 -> return False -- whew!
 		0 -> return True -- wtf?
 		_ -> do
 			-- Try to clean up the extra copy we made
 			-- that has the same name. Egads.
-			_ <- tryIO $ removeFile dest'
+			_ <- tryIO $ removeLink dest
 			return True
 
 -- | Waits as necessary to take a lock.