Return true if cls has on overridable __init__.

def ctor_overridable(cls):
    """Return true if cls has on overridable __init__."""
    prev_init = getattr(cls, "__init__", None)
    if not callable(prev_init):
        return True
    if prev_init in [object.__init__, _auto_init]:
        return True
    if getattr(prev_init, '_clobber_ok', False):
        return True

    print(cls, prev_init, getattr(prev_init, '_clobber_ok', 'missing'))
    return False