SNMP changes/fixes

SNMP changes/fixes
	- changed some snmplib debugging messages
	- simplifed and fixed snmplib_debug_hook interface.  It
	  wasn't properly passing all the 'varargs' args.  Now
	  it just vsnprintf's to a buf and passes that.
	- struct _snmpconf was never used.
	- made 'snmp_agent_conf' a stringlist type
	- moved 'snmp_agent_conf' processing to snmpInit().
	- moved snmpInit() call to before 'ready to serve requests'
	  message.