Make CaseClassSelector consistent with other Expr's

src/main/scala/leon/frontends/scalac/CodeExtraction.scala

src/main/scala/leon/purescala/Constructors.scala

src/main/scala/leon/purescala/Definitions.scala

src/main/scala/leon/purescala/ExprOps.scala

src/main/scala/leon/purescala/Expressions.scala

src/main/scala/leon/purescala/Extractors.scala

src/main/scala/leon/purescala/TypeOps.scala

src/main/scala/leon/synthesis/rules/ADTDual.scala

src/main/scala/leon/synthesis/rules/ADTSplit.scala

src/main/scala/leon/synthesis/rules/DetupleInput.scala

src/main/scala/leon/termination/ChainComparator.scala

src/main/scala/leon/utils/InliningPhase.scala

src/main/scala/leon/verification/InductionTactic.scala