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/asyncio/base_events.py

@@ -151,6 +151,12 @@ class BaseEventLoop(events.AbstractEventLoop):
                 % (self.__class__.__name__, self.is_running(),
                    self.is_closed(), self.get_debug()))
 
+    def create_task(self, coro):
+        """Schedule a coroutine object.
+
+        Return a task object."""
+        return tasks.Task(coro, loop=self)
+
     def _make_socket_transport(self, sock, protocol, waiter=None, *,
                                extra=None, server=None):
         """Create socket transport."""