Add a section heading to AssociationList.java
Add disclaimer about iterators to Dictionary.java
Extended disclaimer about iterators in Dictionary.java
Factor out common code for iterators, mostly to provide design example for students.
Add appropriate citation.
Add citations to OpenHashTable.java
Add citations to Dictionary.java
Add citations to DictionaryIteratorTests.java
Add citations to the code in problems 2 and 3.

Arguably, such citations are not necessary, since it's my code and
it's implicit that I reuse code from the current and previous course
offerings, including from labs and assignments.  However, I've added
the citations to demonstrate good practice.  (It's not great practice -
I haven't given dates of copying and such, but it suffices.)