[ENH] Associations Please review and read the tests ( [er][su] passes new tests, does not break old in clean Squeak3.8g-6548.image )

[rastaehli at mac.com]

This is a good refactoring and bug fix to LookupKey subclasses.  In
clean Squeak3.8g-6548.image before loading the attached change sets, the
number of passed/fail/error tests is 1334/8/3 and after the change sets
the number is 1349/8/3.

apologies if this is a duplicate submission, but I've been having
trouble with first BVAV use.