* re-enable some Z3 extended commands:

* re-enable some Z3 extended commands:
  declare-const
  declare-funs
  declare-preds
  define
  simplify

* don't output --help on bad options, just invite user to try --help

* Datatypes from SMT2 parser now name the tester is-cons (e.g.)

* unknown results produce models, --check-model doesn't fail hard for
  incorrect unknown models.  removed the assert that kept arithmetic
  from producing models if it saw nonlinear

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