asyncio: sync with Tulip

- repr(Task) and repr(CoroWrapper) now also includes where these objects were
  created. If the coroutine is not a generator (don't use "yield from"), use
  the location of the function, not the location of the coro() wrapper.
- Fix create_task(): truncate the traceback to hide the call to create_task().

Lib/asyncio/base_events.py

@@ -155,7 +155,10 @@ class BaseEventLoop(events.AbstractEventLoop):
         """Schedule a coroutine object.
 
         Return a task object."""
-        return tasks.Task(coro, loop=self)
+        task = tasks.Task(coro, loop=self)
+        if task._source_traceback:
+            del task._source_traceback[-1]
+        return task
 
     def _make_socket_transport(self, sock, protocol, waiter=None, *,
                                extra=None, server=None):