properly extract constraints that include logical variables

cp-demo/LazyVars.scala

src/cp/CallTransformation.scala

src/cp/CodeExtraction.scala

src/cp/CodeGeneration.scala

src/cp/ConstraintSolving.scala

src/cp/Extractors.scala

src/cp/LTrees.scala

src/cp/RuntimeMethods.scala

src/cp/Terms.scala

src/cp/Utils.scala

src/purescala/Trees.scala