use openTempFile from file-io

And follow-on changes.

Note that relatedTemplate was changed to operate on a RawFilePath, and
so when it counts the length, it is now the number of bytes, not the
number of code points. This will just make it truncate shorter strings
in some cases, the truncation is still unicode aware.

When not building with the OsPath flag, toOsPath . fromRawFilePath and
fromRawFilePath . fromOsPath do extra conversions back and forth between
String and ByteString. That overhead could be avoided, but that's the
non-optimised build mode, so didn't bother.

Sponsored-by: unqueued

Utility/SshConfig.hs

@@ -28,6 +28,7 @@ import Common
 import Utility.UserInfo
 import Utility.Tmp
 import Utility.FileMode
+import qualified Utility.FileIO as F
 
 import Data.Char
 import Data.Ord
@@ -140,12 +141,12 @@ changeUserSshConfig modifier = do
 			-- If it's a symlink, replace the file it
 			-- points to.
 			f <- catchDefaultIO configfile (canonicalizePath configfile)
-			viaTmp writeSshConfig f c'
+			viaTmp writeSshConfig (toOsPath (toRawFilePath f)) c'
 
-writeSshConfig :: FilePath -> String -> IO ()
+writeSshConfig :: OsPath -> String -> IO ()
 writeSshConfig f s = do
-	writeFile f s
-	setSshConfigMode (toRawFilePath f)
+	F.writeFile' f (encodeBS s)
+	setSshConfigMode (fromOsPath f)
 
 {- Ensure that the ssh config file lacks any group or other write bits, 
  - since ssh is paranoid about not working if other users can write