HK2-157.  Wow.  Getting rid of this classloader leak was tough.  The final
fix involves PhantomReferences and SoftReferences and changes to 5 different
caches. There still may be more, I'm going to do an inventory of the code
to find others.  However, I think the current solution removes the leak,
is fairly efficient in the normal case and does not have the cache grow
without bound (by removing removed classes when the PhantomReference notices
classes go)