various fixes to translation of case classes with set/map fields

src/cp/CodeGeneration.scala

src/purescala/AbstractZ3Solver.scala

src/purescala/Evaluator.scala

src/purescala/FairZ3Solver.scala

src/purescala/Trees.scala

src/purescala/Z3ModelReconstruction.scala

src/purescala/Z3Solver.scala

src/purescala/z3plugins/instantiator/Instantiator.scala