new HashedSet + WeakHashedSet classes

I have now finished the two new classes HashedSet and WeakHashedSet. I 
have added some tests for them, though I should add a lot more.

To make this work I needed to make a few changes to AbstractHashedMap. 
These changes had a few repercussions on other classes. But they now 
run all the tests successfully.

They classes with UML diagrams and some explanations are available on 
my web site at:
http://bblfish.net/java/collections/


Please let me know if this is the wrong place to post this.

Thanks,

Henry Story