[cpp-threads] modes, pass 2

[Doug Lea]

> 
> 
> I don't understand fallible_*,

It means that CAS can return false just because it feels like it.
Like LL/SC does on all platforms I know that use it.


  and I don't understand *_ordered. Sorry. :-)

Actually, I think you don't understand the sense of "release". Sorry.
It's the main reason I apologized for crummy names.
Here, release is intended to ensure that read-after-write
works, which entails a heavy storeLoad barrier.

Better names would be very very welcome.

-Doug