Multicore download failed on windows

@lpenasa reported that kernels download (in TourConfig or MetaKernel) on windows is not possible and raise a RunttimeError:

RuntimeError:
        An attempt has been made to start a new process before the
        current process has finished its bootstrapping phase.

        This probably means that you are not using fork to start your
        child processes and you have forgotten to use the proper idiom
        in the main module:

            if __name__ == '__main__':
                freeze_support()
                ...

        The "freeze_support()" line can be omitted if the program
        is not going to be frozen to produce an executable.         

The error comes from MetaKernel.check() function that use multiprocessing.Pool.

This is a known issue and not directly related to planetary-coverage 👉 cf. stackoverflow.