withFile defeats dead handle closure

withFile keeps the handle it creates alive until the user action completes. If we want to avoid this, we can. All that's required is to capture the weak reference that holds the handle's finalizer. Then instead of closing the handle in the end (or on exception) using hClose, withFile can run the handle's finalizer. Should we do this? Or does it run too much against the idea that handles should be managed as explicitly as possible?