Fix fibers::asio::round_robin's notify() method.

[xaqq]

The notify() method of fibers::asio::round_robin doesn't give
a chance to pending fibers to run.

See #100 for more detail.

[olk]

Implementation of has already changed, see branch develop

[xaqq]

In develop, notify() simply set the timer to expires, and it seems its not enough.

[olk]

you are right - Nat and I tried to get asio::round_robin working with multiple threads running io_service::run() of one instance of io_service. Unfortunately io_service it didn't work and not all changes were rolled back.
I'll take you example and add it to the library too - could you tell me your Name?

[olk]

merge must be into branch develop first - please change your pull request or tell me if I should do it (format-patch etc).

[xaqq]

I changed the base on github, but it looks like it did something ugly. Feel free to close the PR and cherry-pick the commit or something if that keeps history cleaner.

Bear in mind that while this change seems to positively affect the example from #100 I think I'm still observing suspicious behavior when running my real program through valgrind. (with the use case being 2 io_service on 2 thread).

My name's Arnaud Kapp.

[olk]

Arnaud, regarding to valgrind please apply valgrind=on at cmd-line.
(see http://www.boost.org/doc/libs/1_62_0/libs/context/doc/html/context/stack/valgrind.html)

[olk]

pushed to branch develop

[xaqq]

Thanks.

WRT valgrind, I already use valgrind=on. The issue is not invalid memory access / "client switching stack". Rather it looks like spinning. I can't reproduce w/o valgrind so it's a bit weird.
I'll report back if I find something.