imperative transformation working with if then else and assignment

mytest/IfExpr1.scala

src/main/scala/leon/Analysis.scala

src/main/scala/leon/ImperativeCodeElimination.scala

src/main/scala/leon/plugin/Extractors.scala

src/main/scala/leon/purescala/PrettyPrinter.scala

src/main/scala/leon/purescala/Trees.scala