Exit gracefully when using a non-fates restart file to interpolate to a simulation with fates

You can't use a non-fates restart file to interpolate initial conditions to a simulation with fates. I don't think we will fix this, but we want to document it. And also add some general ability in so this won't happen out of the box. So for a fates simulation the model shouldn't try to interpolate from non-fates initial conditions. And because of #211 it shouldn't try to interpolate from a fates restart file either.