Mass ordering check omega check
This MR builds upon !8 (merged) (i.e. it's a branch of it) and adds another test to check that
Omega-vs-time is monotonic.
@edward.fauchon-jones I've added it as a
format2Interfield check which isn't strictly true...
But I think it's fine. Not perfect. Do you think we should add another test field?
My build is breaking too. I can't figure out why. When you get a chance it would be great if you could take a look.