Adding merge sort benchmarks. They expose some bugs in the transformation. Fix them!

src/main/scala/leon/Main.scala

src/main/scala/leon/invariant/engine/SpecInstatiator.scala

src/main/scala/leon/invariant/util/Util.scala

src/main/scala/leon/laziness/ClosurePreAsserter.scala

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

src/main/scala/leon/laziness/LazinessUtil.scala

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

src/main/scala/leon/laziness/TypeRectifier.scala

src/main/scala/leon/solvers/z3/AbstractZ3Solver.scala

testcases/lazy-datastructures/BottomUpMegeSort.scala

testcases/lazy-datastructures/LazyMegeSort-edited.scala

testcases/lazy-datastructures/LazyMegeSort.scala