Freeze random seed

[keithw]

It might be a good idea to fix the random seed used for the 250,000 realizations of the simulation, in case readers are interested in reproducing exactly the numbers reported on the NYT Upshot Web site.

I have tried with today's data and cannot quite match the figures on the Web site. For example, even after trying several times, I can't get up to >88.5% for New Hampshire. (The public figure is 89.)

But there is some run-to-run slop that comes from the randomness, and it would be easier to debug if I knew I was using the same random seed as the public figures.