tuned;

prefer Isabelle/Scala Future;

clarified modules;

--HG--
rename : src/Pure/Concurrent/simple_thread.ML => src/Pure/Concurrent/standard_thread.ML
rename : src/Pure/Concurrent/simple_thread.scala => src/Pure/Concurrent/standard_thread.scala

tuned;

added Par_List in Scala, in accordance to ML version;
system property "isabelle.threads" determines size of Scala thread pool, like system option "threads" for ML;
avoid ".par" framework with its hard-wired thread pool, which also has problems with cancellation;
tuned;