[isabelle-dev] scala-2.11.0

[Makarius]

The Scala guys have released scala-2.11.0, and we are using it since 
Isabelle/5d629da46f04.  This requires the usual "isabelle components -a".

Moreover, there is some chance that sticky JVM jam from old jars is 
getting in the way.  In the case of odd Java/Scala startup failures 
(exceptions about classes that could not be loaded), the following 
directories need to be purged manually and carefully:

   * within $ISABELLE_HOME:

     lib/classes/
     src/Tools/jEdit/dist/

   * within $ISABELLE_HOME_USER

     jedit/jars-cache

I have also taken the opportunity to brush up the general Isabelle/Scala 
view on the Scala system and library (presently at Isabelle/70cc1164fb83). 
The main omission is the remaining use of the old actors framework, which 
was the latest and greatest thing a few years ago and is now obsolete -- 
Scala code decay is much faster than we are used to in our ML world.

I am presently considering to discontinue actors altogether, and merely 
use the thread task pool, explicit threads, and typed channels between 
them.  But I also need to see how Akka actors do it today, to get a few 
more ideas, before trimming it down to the simplest possible approach.


 	Makarius