What happens in the following case:
- I mark a local as to-be-closed,
- then this is used as upvalue for an enclosed function,
- then the function returns the enclosed function
- a closure is created: the upvalue is moved from the stack to the heap
- ...and here is where I do not know what happens: is the local/upvalue out of scope now?
- ...does _close() get executed or not?
