SNMP Checks| Extended type fix

Dynamically loaded class comparison doesn't work
Accessing python's hidden attributes is freaking ugly but the clean way
(ASN1 isSameTypeWith) doesn't work because CounterBasedGauge64 (a gauge) match
with both ZeroBasedCounter64 and Counter64 ( counters ), given that
these classes are just passthrough
see sources at
http://nullege.com/codes/show/src@pysnmp-mibs-0.0.8a@pysnmp_mibs@HCNUM-TC.py