[SNMP4J] more frequent save of persistence

[Clement_Pellerin at ibi.com]

I save the persistent state when my application terminates, but if the application crashes or is forcibly stopped, all non-volatile changes are lost. Is the DefaultMOPersistenceProvider thread-safe if I call it when the agent is still running? Is there a way to determine when the persistent state was modified, to schedule a save soon after? Sure I could schedule the save at regular intervals, but I would feel more comfortable if I could save very soon after a password is changed. Our MIB is completely volatile, so I'm mostly concerned with the standard MIBs implemented by SNMP4J itself.