Improve debugging for trees. asString now preferred over toString.

src/main/scala/leon/LeonOption.scala

src/main/scala/leon/Reporter.scala

src/main/scala/leon/Settings.scala

src/main/scala/leon/codegen/runtime/ChooseEntryPoint.scala

src/main/scala/leon/evaluators/RecursiveEvaluator.scala

src/main/scala/leon/purescala/Common.scala

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

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

src/main/scala/leon/purescala/PrinterOptions.scala

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

src/main/scala/leon/purescala/TypeTrees.scala

src/main/scala/leon/solvers/Solver.scala

src/main/scala/leon/solvers/combinators/DNFSolver.scala

...main/scala/leon/solvers/combinators/UnrollingSolver.scala

src/main/scala/leon/synthesis/Rules.scala

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

src/main/scala/leon/termination/ChainProcessor.scala

src/main/scala/leon/termination/Processor.scala

src/main/scala/leon/utils/DebugSections.scala

src/main/scala/leon/verification/AnalysisPhase.scala