perl termination fixes:

*) master exit hook is run before global pool cleanup, so call PERL_SYS_TERM()
   after perl_destruct()/perl_free().  This fixes the message
        panic: MUTEX_LOCK (22) [op.c:352]
   on some threaded perl builds

*) call perl_destruct()/perl_free() before PERL_SYS_TERM() for
   non-mulitiplicity perl