SBV prover backends abstract over ExtCns variables with non-function types.
SBV prover backends abstract over ExtCns variables with non-function types.

This ensures that variables from fresh_symbolic will appear in the
counterexample models returned by SBV.

Fixes #125.

GaloisInc/saw-script,GaloisInc/saw-script,GaloisInc/saw-script,GaloisInc/saw-script,GaloisInc/saw-script