[Async-sig] asyncio.timeout() is not portable

[Yury Selivanov]

> On Jun 9, 2016, at 12:38 AM, Andrew Svetlov <andrew.svetlov at gmail.com> wrote:
> 
> My first thought was to use `async with` but I found that just `with` also works.
> 
> Sorry, but I don't follow how async context manager may be better.

It would make asyncio.timeout() usable only inside coroutines.  Using
it outside of a coroutine is an error anyways.

Yury