…ng.ThreadLocal

  for thread-transactor mapping instead.

…script objects/functions.

…ctually

  stop the right thread in kill() and implement isAlive().
* Add some javadoc comments.

…) but throws an

  IllegalStateException if no Transactor exists for the current thread.
* Use Transactor.getInstanceOrFail() in cases where we need a Transactor, but want to 
  fail instead of creating one when none exists.

* Fix RequestEvaluator.stopTransactor() to actually operate on the right 
  thread and transactor. This requires introducing an additional transactor field.
* Move ScriptingEngine.exitContext() to finally clause to make sure we exit the 
  context even when an exception is thrown.
* Add some javadoc fluff to ScriptingEngine.

…d with the current thread,

  creating local transactions if necessary.

* Add code for observeInstructionCount() but leave it commented out for now.