Express "not equal" constraints

[bmaclach]

Currently in Drasil, constraints can either be expressed as a Range, EnumeratedReal, or EnumeratedStr.

Another type of constraint we need to express are constraints that something does not equal a certain value. For example, in SSP we have the constraint that the size of the list x_wt cannot equal 1.

This could be constructed by a couple of Range constraints (one range for everything below 1, and another for everything above 1), but that seems like a hack.

[JacquesCarette]

So the list can be empty? That's odd.

[bmaclach]

Yes. The water table may not exist (i.e. the slope is dry).

[JacquesCarette]

So I can't help but wonder if this is kind of an artificial constraint, in that this constraint is an artifact of the current encoding of the problem, and that a different encoding would not need this. [Just trying to prioritize things.]

[JacquesCarette]

Like #1800. But this one might require a design first, before going ahead with an implementation.