> Why isfuture() is moved, and asyncio.coroutine uses
> base_futures.isfuture() instead of futures.isfuture()?

Import cycles: 

- `_asyncio` module is now being imported from `futures.py`
- and `_asyncio` is now imported from `tasks.py`; 
- and `tasks.py` imports `futures.py` to have `isfuture`.

Long story short, I don't see a way of keeping `isfuture` in `futures.py`.  The easiest option is to have it in a separate module.