Allow MIBjig to become a master agent

These changes allow MIBjig to be the master agent on its own, without having to connect via AgentX and without having to worry about conflicts with the master SNMP server overriding the MIBs that MIBjig wants to serve -- e.g., making it easier to provide your own sysDescr, or sysObjectID, or whatever your NMS might be using for auto-discovery.