Integrating unique references

src/main/scala/leon/laziness/FreeVariableFactory.scala

src/main/scala/leon/laziness/LazinessEliminationPhase.scala

src/main/scala/leon/laziness/LazyClosureConverter.scala

src/main/scala/leon/laziness/LazyExpressionLifter.scala

src/main/scala/leon/laziness/LazyFunctionsManager.scala

src/main/scala/leon/laziness/LazyVerificationPhase.scala

testcases/lazy-datastructures/ManualnOutdated/Concat.scala