Change the default job termination behaviour to idle_timeout=0

Many users cannot understand why for order driven jobs the tasks are not automatically terminated, see http://sourceforge.net/forum/forum.php?thread_id=1800467&forum_id=486122

I suggest to change the default behaviour to the setting of <job idle_timeout="0">. The present behaviour (not terminating) could be restored by any of <job idle_timeout=""> or <job idle_timeout="no">, <job idle_timeout="false">.

Any objections?