1. aclose() should not propagate StopAsyncIteration:

  async def agen():
     try:
        yield
     except: 
        pass
  gen = agen()
  await agen.asend(None)
  await agen.aclose()  # <- this shouldn't raise StopAsyncIteration

2. athrow() should propagate StopAsyncIteration when the exception was swallowed by the generator and it returned:

  async def agen():
     try:
        yield
     except: 
        pass
  gen = agen()
  await agen.asend(None)
  await agen.athrow(ValueError)  # <- this should raise StopAsyncIteration