snmpit now discovers which switch to operate on based on the members of the
VLANs it is to operate on. This is only a temporary multi-switch solution, as it only picks one switch to operate on. Also, added a sanity check in snmpit_cisco.pm. Now checks every port that it controls, to make sure it's on the right switch. If this sanity check fails, dies to prevent any damage to existing switch configuration.