Boost FunDef.duplicate, get rid of FunDef.copyContentFrom

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

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

src/main/scala/leon/purescala/FunctionClosure.scala

src/main/scala/leon/purescala/MethodLifting.scala

src/main/scala/leon/purescala/RestoreMethods.scala

src/main/scala/leon/purescala/ScopeSimplifier.scala

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

src/main/scala/leon/solvers/isabelle/AdaptationPhase.scala

src/main/scala/leon/synthesis/Synthesizer.scala

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

src/main/scala/leon/termination/TerminationChecker.scala

src/main/scala/leon/utils/UnitElimination.scala