Change index ordering in rtvd related routines. Thanks go to Mariusz Mam...

Changing index ordering from (variable, spatial) to (spatial, variable) yields approximate ~20% speedup. I have no idea we we haven't checked it for so long... Probably we could squeez out more if similar changes will be made outside of *sweeps* scope. Following changes were inspired by a discussion with @mmamon, all kudos go to him.