Changed AbstractSnmpValue so that ISO-8859-1 strings are accepted as "displayable".
Fixes bug NMS-5281. Also changed the handling of 63-bit hexstring counters in the
FCMGMT-MIB so that we don't accidentally try to handle 8-digit decimal values as
weird FCMGMT counters. Fixes bug NMS-6202.

Conflicts:
	core/snmp/api/src/main/java/org/opennms/netmgt/snmp/AbstractSnmpValue.java
	core/snmp/api/src/main/java/org/opennms/netmgt/snmp/SnmpUtils.java
	opennms-services/src/main/java/org/opennms/netmgt/collectd/SnmpAttribute.java