Add a division-of-constants reduction rule.

[Linas Vepštas]

Add a contin reduction that can reduce this:

((5.06447865729134317 * x) - 1.38413811600397763)  > 0

to this:

(x - 0.2733031788002957) > 0

Such a rule does not currently exist, because when contins used the power-of-2 representation, performing constant divisions would blow up the rep (consider representing 1/3 by base-2 binary!)

Now that we use float-poit and PSO, it makes sense to add this new reduction rule.