ruby: Fix memWriteback() not to record auto-delete events
Currently ruby memWriteback() hijacks the event queue to perform its flushing

events by descheduling everything, flushing, then restoring everything again.

However, events with the AutoDelete flag set will delete themselves when they

are descheduled, causing an error when attempting to schedule them again.

This is fixed by simply not recording them when taking them off the queue.  A

new warning lets the user know that ruby memWriteback() may cause problems if

simulation continues.