DynamicList
-----------
- construction, assignment and append
HashSet
-------
- construction, insert, set.
- assignment will use the implicit List constructor
hashedWordList
--------------
- construction, assignment
- additional sort() and uniq() methods.
- Readonly access to HashTable information via lookup() method.
- NB: could avoid 'const char**' constructors in the future
- operator+= : add in the listed keys
- operator-= : remove the listed keys
- operator&= : intersection of keys
- added xfer constructor (just in case)
- moved labelHashSet typedef to HashSet.H, for consistency with the
wordHashSet typedef being there and since it is used so often