Query service ejb test

Hi Gunter.  This is the fix for the broken unit-tests that you mentioned last week. You might notice that I refactored some of the code in QueryServiceEJB to

A) make unit-testing easier by
B) reducing duplication and 
C) breaking the logic into smaller less-complex methods.

While writing the tests, I noticed some questionable logic.  I wrote a note to you on that, and I'll point out the code here.
I'm not sure about the logic here.  What is the expected behaviour, for example, when this method is called three times, with tuples that have externalRetrieveAET equal to "A", "B", and "C"?  My expectation is that we want to keep CommonAttributes#externalRetrieveAET as null, but with this logic it will be "C"?