PICKED FROM TRUNK 21165

fix for SCHEDULING-1436 for Matlab and Scilab

added the PAjobRemove function for Matlab & Scilab to manually remove jobs

added the "RemoveJobAfterRetrieve" option to configure the behavior of automatically removing jobs or not (default to on).

added the PAisConnected() check before any interaction with the scheduler (error if not).

git-svn-id: svn+ssh://scm.gforge.inria.fr/svn/proactive/scheduling/branches/Scheduling_3.1.x@21211 28e8926c-6b08-0410-baaa-805c5e19b8d6