about "mib-2" and some others.  This is defined in SNMPv2-SMI which wasn't
in the list of MIB files and is needed by SNMPv2-MIB.  But, it probably
shouldn't need to be explicitly included, since there is an IMPORT of the
symbols in question at the beginning of SNMPv2-MIB.  But I added it to
the SNMP::addMibFiles() arguments anyway.

This came about because I was messing with PowerNet-MIB.txt to support the
7960 power controllers (we have an 8 year old version of that file).