mp.set_start_method("spawn") targets wrong module

[nkemnitz]

The code currently uses the standard libraries multiprocessing.set_start_method. But when calling pathos.pools.ProcessPool, this is never recognized, because pathos internally uses a fork of the stdlib called multiprocess.

I think switching to import multiprocess as mp is the quickest fix and would also avoid mixing multiprocessing.Queue (stdlib) with the pathos stuff