Test failing on Python 3.6

[Jenselme]

One test is failing on Python 3.6: test_chained_callback Tested on Python 3.6.0rc

________________________________________________________________________ test_chained_callback[asyncio] ________________________________________________________________________

framework = <module 'txaio.aio' from '/txaio/txaio/aio.py'>

    def test_chained_callback(framework):
        """
        Chain two callbacks where the first one alters the value.
        """
        calls = []
    
        def callback0(arg):
            print('callback 0', arg)
            calls.append(arg)
            return arg + " pray I do not alter it futher"
    
        def callback1(arg):
            print('callback 1', arg)
            calls.append(arg)
    
        f = txaio.create_future()
        txaio.add_callbacks(f, callback0, None)
        txaio.add_callbacks(f, callback1, None)
        txaio.resolve(f, "the deal")
    
        run_once()
    
        assert len(calls) == 2
        assert calls[0] == "the deal"
>       assert calls[1] == "the deal pray I do not alter it futher"
E       assert 'the deal' == 'the deal pray I do not alter it futher'
E         - the deal
E         + the deal pray I do not alter it futher

test/test_callback.py:86: AssertionError

[oberstet]

It fails on Python 3.6 both for Twisted and asyncio: https://travis-ci.org/crossbario/txaio/builds/192086131

So there definitely is an issue - needs investigation ..

[oberstet]

fixed via #104