Revamped concurrency API

[Andrei Alexandrescu]

MIURA Masahiro wrote:
> Jeremie Pelletier wrote:
>> I also don't believe one model is "ruling them all".
> 
> Let me clarity this, just in case I have caused an unnecessary
> confusion:  I think Sean's Erlang-like API is meant to coexist
> with the current core.thread, and that you can use one or both
> of them to build higher-level concurrency models.
> 
> I think it's nice to have core.thread *and* message-passing API
> in Phobos.  Thread alone is too primitive for daily use, but
> we don't want to have too many concurrency models.

Absolutely! I agree. We need to attack the beast with everything we have.	

Andrei