Altered code to properly handle asymmetric twin swing dice

Fixes #1467.

http://jenkins.buttonweavers.com:8080/job/buttonmen-blackshadowshade/555/
I'm on the fence about passing along the subdie values via the API.  I guess there's no *harm* in it (as long as you protect them during swing setting and so forth, which my read of the code changes is that you do), so what the heck.