asyncio: sync with Tulip

- Tulip issue 185: Add a create_task() method to event loops. The create_task()
  method can be overriden in custom event loop to implement their own task
  class. For example, greenio and Pulsar projects use their own task class. The
  create_task() method is now preferred over creating directly task using the
  Task class.
- tests: fix a warning
- fix typo in the name of a test function
- Update AbstractEventLoop: add new event loop methods; update also the unit test

Lib/test/test_asyncio/test_tasks.py

@@ -233,6 +233,9 @@ class TaskTests(test_utils.TestCase):
         self.assertRegex(repr(task),
                          '<Task .* wait_for=%s>' % re.escape(repr(fut)))
 
+        fut.set_result(None)
+        self.loop.run_until_complete(task)
+
     def test_task_basics(self):
         @asyncio.coroutine
         def outer():