Remove some dead code

* The following modules are no longer used and have been removed completely:

	GF.Compile.Compute.ConcreteLazy
	GF.Compile.Compute.ConcreteStrict
	GF.Compile.Refresh

* The STM monad has been commented out. It was only used in
  GF.Compile.SubExpOpt, where could be replaced with a plain State monad,
  since no error handling was needed. One of the functions was hardwired to
  the Err monad, but did in fact not use error handling, so it was turned
  into a pure function.

* The function errVal has been renamed to fromErr (since it is analogous to
  fromMaybe).

* Replaced 'fail' with 'raise' and 'return ()' with 'done' in a few places.

* Some additional old code that was already commented out has been removed.

src/compiler/GF/CompileInParallel.hs

@@ -66,7 +66,7 @@ batchCompile1 lib_dir (opts,filepaths) =
      let rel = relativeTo lib_dir cwd
          prelude_dir = lib_dir</>"prelude"
          gfoDir = flag optGFODir opts
-     maybe (return ()) (D.createDirectoryIfMissing True) gfoDir
+     maybe done (D.createDirectoryIfMissing True) gfoDir
 {-
      liftIO $ writeFile (maybe "" id gfoDir</>"paths")
                         (unlines . map (unwords . map rel) . nub $ map snd filepaths)
@@ -213,14 +213,14 @@ instance (Functor m,Monad m) => Applicative (CollectOutput m) where
   (<*>) = ap
 
 instance Monad m => Monad (CollectOutput m) where
-  return x = CO (return (return (),x))
+  return x = CO (return (done,x))
   CO m >>= f = CO $ do (o1,x) <- m
                        let CO m2 = f x
                        (o2,y) <- m2
                        return (o1>>o2,y)
 instance MonadIO m => MonadIO (CollectOutput m) where
   liftIO io = CO $ do x <- liftIO io
-                      return (return (),x)
+                      return (done,x)
 
 instance Output m => Output (CollectOutput m) where
   ePutStr   s = CO (return (ePutStr s,()))