castro.update_sources_after_reflux doesn't make sense for MOL/new SDC

[zingale]

The castro.update_sources_after_reflux functionality uses the "new" source stuff, and does the corrector after the flux correction. But for MOL (and new SDC) integration, we don't ever use the new source logic, the source terms are applied at the integration stage in the integrator, so it is not clear that this logic works for these integration methods.

We should skip this step for these updates.

[maxpkatz]

I'm OK with disabling it in this case as it is clearly wrong, but please leave this issue open after we merge #545. I'd like to investigate whether it's possible to fix update_sources_after_reflux for these integration methods.

[zingale]

sure. I was thinking about that as well.

[maxpkatz]

My initial thought was that since the final time node is always n+1 (right?) then we could just re-evaluate the old sources and add the appropriate weighting.

[zingale]

To get the same formal order of accuracy as the integration method, we would need to correct each stage of the integrator, I think.