Right now when you want to use `subprocess.STARTUPINFO`, you need to do something like this: 

    si = subprocess.STARTUPINFO()
    si.dwFlags = subprocess.STARTF_USESTDHANDLES
    subprocess.Popen(['whatever'], startupinfo=si)

It would be much nicer to do this: 

    subprocess.Popen(
        ['whatever'],
        startupinfo=subprocess.STARTUPINFO(
            subprocess.STARTF_USESTDHANDLES
        )
    )

So I suggest that the `STARTUPINFO` constructor take an optional argument that sets the flags on it.