Amr/Advection_AmrCore: istep & t_new not set for new finer levels after regrid

[mirenradia]

After regridding, the code sets dt on any new finer levels that are created (see here). Shouldn't it also set istep and t_new as well?

[WeiqunZhang]

t_new is set in AmrCoreAdv::MakeNewLevelFromCoarse. As for istep, I guess it depends on how to interpret its meaning.