even more cleaning up

src/main/scala/purescala/Extensions.scala

src/main/scala/purescala/Settings.scala

src/main/scala/purescala/Z3Solver.scala

src/main/scala/purescala/testcases/Main.scala

...rescala/z3plugins/instantiator/AbstractInstantiator.scala

...scala/purescala/z3plugins/instantiator/Instantiator.scala