First chunk of boolean-terms support.

First chunk of boolean-terms support.

Passes simple tests and doesn't break existing functionality.
Still need some work merged in for models.

This version enables BV except for pure arithmetic (since we might otherwise need Boolean term support, which uses BV).  Tonight's nightly regression run should tell us if/how that hurts performance.

(this commit was certified error- and warning-free by the test-and-commit script.)