updated according to scala-2.11.0 recommendations;

--- a/src/Pure/library.scala	Wed Apr 23 13:28:32 2014 +0200
+++ b/src/Pure/library.scala	Wed Apr 23 14:16:08 2014 +0200
@@ -186,5 +186,5 @@
     new java.util.concurrent.Callable[A] { def call = f() }
 
   val default_thread_pool =
-    scala.collection.parallel.ThreadPoolTasks.defaultThreadPool
+    scala.collection.parallel.ForkJoinTasks.defaultForkJoinPool
 }