base class Joiner with derived class JoinerOld

[WilkAndy]

Or something like that - JoinerOld seems to extend Joiner basically. Tagging @cpgr.

[cpgr]

i think that this could probably be condensed into a single class that assembles the appropriate vectors (density, density old, viscosity, real perm if needed etc).

[WilkAndy]

That would certainly be best. I don't know how to do it though - i think we want the "old" to be optional.

[cpgr]

I'll have a go at this tomorrow morning and let you know how it goes.