port runtests.py to Python 2.7
port greenio to Python 2 and Trollius
port tests to Python 2 and Trollius
Fix test_tasks.py on Python 3.3
fix yield_from() on Python 2 for exc.__traceback__
get TestCase from Trollius to get assertRaisesRegex
Trollius coroutines must use "yield From()"
trollius: modify task_factory to build GreenTask
Fix test_task_yield_from_invalid() on Trollius
replace task_factory with create_task() method
Fix test_task_yield_from_invalid() with asyncio
prefer asyncio over trollius

- add GreenTrolliusEventLoopPolicy for Trollius which creates tasks
  compatible with Trollius
- yield_from() now also accepts coroutine objects, so the caller doesn't
  have to create a task object (which may not be compatible with asyncio
  *and* trollius)
Test features instead of testing the Python version
Fix greenio.task()

- with asyncio, greenio.task(coro) now creates GreenTask, not Task
- move the "if trollius is not None:" out of the function, add
  _create_task() function
I moved Python 2 changes in a new pull request