New nonlinear expression stuff doesn't support min properly

[davidanthoff]

On master with the new non linear expression, one cannot call min on two AffExpr because min internally just calls isless, and that is one of the functions that doesn't have operator overloading for the JuMP expression types.

I think the solution is presumably that JuMP needs to add a min method that internally uses JuMP.op_strictly_less_than (or one of its variants), right?

[odow]

Oops. This was just an oversight. I added min and max support to MOI after I had started working on #3106 and never copied across the new features...the perils of working on a branch for one year.

See #3509