Include classdef in method call, to extract method return types

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

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

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

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

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