asyncio: sync with Tulip

- Sort imports
- Simplify/optimize iscoroutine(). Inline inspect.isgenerator(obj): replace it
  with isinstance(obj, types.GeneratorType)
- CoroWrapper: check at runtime if Python has the yield-from bug #21209.  If
  Python has the bug, check if CoroWrapper.send() was called by yield-from to
  decide if parameters must be unpacked or not.
- Fix "Task was destroyed but it is pending!" warning in
  test_task_source_traceback()
asyncio: sync with Tulip

- Sort imports
- Simplify/optimize iscoroutine(). Inline inspect.isgenerator(obj): replace it
  with isinstance(obj, types.GeneratorType)
- CoroWrapper: check at runtime if Python has the yield-from bug #21209.  If
  Python has the bug, check if CoroWrapper.send() was called by yield-from to
  decide if parameters must be unpacked or not.
- Fix "Task was destroyed but it is pending!" warning in
  test_task_source_traceback()
Issue #21163: BaseEventLoop.run_until_complete() and test_utils.run_briefly()
don't log the "destroy pending task" message anymore. The log is redundant for
run_until_complete() and useless in run_briefly().
(Merge 3.4) Issue #21163: BaseEventLoop.run_until_complete() and
test_utils.run_briefly() don't log the "destroy pending task" message anymore.
The log is redundant for run_until_complete() and useless in run_briefly().
Issue #21882: In turtle demos, remove module scope gui and sys calls by
either deleting or moving to the module's main function.
Merge with 3.4
Issue #18592: Add unittests for SearchDialogBase. Patch by Phil Webster.
Merge with 3.4
Issue #13689: Remove a dead link from howto/urllib.
Issue #13689: Merge from 3.4.
Issue #18592: Refactor 2 SearchDialogBase.create_(option/other)_buttons methods
to remove duplication and return info for tests.  Rewrite corresponding tests.
Test_create_option_buttons was not testing anything because of buggy
comparisons.  Use Python subscripting to get widget options.
Merge with 3.4