PrefixedNameSet implementation suitable for storing small set of PrefixedName values (generally 8 or less). Uses linear search, and is thus the most compact presentation for a set

Notes about usage:

• All Strings contained in PrefixedName instances are assumed interned, so that equality comparison can be done (both for values stored and keys used)
• It is assumed that sets are never empty, ie. always contain at least one entry.
• It is assumed that caller has ensured that there are no duplicates in the set -- this data structure does no further validation.