TransformerWithPaths now traverses Ensuring
DefaultTactic.generatePreconditions and generateCorrectnessConditions now looks in fullBody
Fix CodeGeneration to handle Require
Don't collect Require, Ensuring in collectCorrectnessConditions

((), Nil()) passes {
  case () => Cons(0, Nil())
}

was true(!) because Nil </: Cons and Cons </: Nil which caused the case
to filtered out silently.

Translation from String to List[Char] for Z3 on demand.

Added missing strings in enumeration.
Better error messages when tests fail.

corrected a web benchmark.

Removed warnings from SelfPrettyPrinter.