Fix tests on PYPY about circuits

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New error is:

=================================== FAILURES ===================================
_____________________________________ test _____________________________________
manager = <Manager/ 3642:MainThread (queued=2) [R]>
watcher = <Watcher/* 3642:MainThread (queued=0) [S]>
    def test(manager, watcher):
        app = App()
        process, bridge = app.start(process=True, link=manager)
>       assert watcher.wait("ready")
E       AssertionError: assert False
E        +  where False = <bound method Watcher.wait of <Watcher/* 3642:MainThread (queued=0) [S]>>('ready')
E        +    where <bound method Watcher.wait of <Watcher/* 3642:MainThread (queued=0) [S]>> = <Watcher/* 3642:MainThread (queued=0) [S]>.wait
tests/core/test_bridge.py:26: AssertionError

https://travis-ci.org/circuits/circuits/jobs/552766578

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Works meanwhile.