Changed exceptions from SNMP tree to consolidate down to one OID not
found exception. Index based functions no longer check bounds or throw
checked exceptions. General code cleanup and refactoring.
Cleaned up argument checking in SnmpTree. Removed comparator for in
SnmpTreeConstructor as SnmpLookupField is comparable.
Changed tree merge logic to no longer do an array merge since frequency
of merge should be infrequent.
Minor cleanup.