(1) Refactor concurrency, (2) write to .gfo.tmp then rename to .gfo

(1) introduces the module GF.Infra.Concurreny with lifted concurrency
    operators (to reduce uses of liftIO) and some additional concurrency
    utilities, e.g. a function for sequential logging that is used in
    both GF.CompileInParallel and GFServer.
(2) avoids leaving broken .gfo files behind if compilation is aborted.

src/compiler/GF/System/Directory.hs

@@ -7,7 +7,7 @@ import System.Directory as D
        hiding (canonicalizePath,createDirectoryIfMissing,
                doesDirectoryExist,doesFileExist,getModificationTime,
                getCurrentDirectory,getDirectoryContents,getPermissions,
-               removeFile)
+               removeFile,renameFile)
 import Data.Time.Compat
 
 canonicalizePath path = liftIO $ D.canonicalizePath path
@@ -21,4 +21,5 @@ getCurrentDirectory :: MonadIO io => io FilePath
 getCurrentDirectory = liftIO D.getCurrentDirectory
 getPermissions path = liftIO $ D.getPermissions path
 
-removeFile path = liftIO $ D.removeFile path
+removeFile path = liftIO $ D.removeFile path
+renameFile path = liftIO . D.renameFile path