Fix instances of Reify and Reflect for lists of references.

[facundominguez]

These instances used to work when reify j produced a global reference of j. But now, reify [j] will delete the very local references that it is returning, and reflect [j] will delete the input j likely surprising the user.

Perhaps reify and reflect could be fixed by using local frames depending on how expensive they are.

  instance Reify a => Reify [a] where
    reify jobj = do
        n <- getArrayLength jobj
        forM [0..n-1] $ \i -> do
          jx <- getObjectArrayElement jobj i
          x  <- reify jx
          deleteLocalRef jx
          return x

  instance Reflect a => Reflect [a] where
    reflect xs = do
      let n = fromIntegral (length xs)
      array <- newArray n :: IO (J ('Array (Interp a)))
      forM_ (zip [0..n-1] xs) $ \(i, x) -> do
        jx <- reflect x
        setObjectArrayElement array i jx
        deleteLocalRef jx
      return array