
Synchronously receive results from two sub processes 
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Use MultiChannels for receiving multiple results from remote code::

    >>> import execnet
    >>> ch1 = execnet.PopenGateway().remote_exec("channel.send(1)")
    >>> ch2 = execnet.PopenGateway().remote_exec("channel.send(2)")
    >>> mch = execnet.MultiChannel([ch1, ch2])
    >>> l = mch.receive_each()
    >>> assert len(l) == 2
    >>> assert 1 in l 
    >>> assert 2 in l 
