Port greenio to Trollius

Hi,

I would like to use greenio in OpenStack to be able to use the asyncio API be execute tasks in greenlet. OpenStack projects are heavily based on eventlet and it's not possible to switch from eventlet to asyncio in one step, it should be done incrementally.

asyncio and Python 3 cannot be requirements on OpenStack because OpenStack is already deployed in production with Python 2, and projects don't support Python 3 yet (most clients are Python 3 compatibility, but not servers yet).

My plan is to use Trollius with greenio, replace incrementally eventlet with Trollius in OpenStack:
http://haypo-notes.readthedocs.org/openstack.html#roadmap

Victor
I understand that, that's the part that feels wrong, big ``#ifdef trollius`` around blocks of code.

But I guess this is how it goes....