TJ: another edge case, still fails.
JPM/TJ: Lucene.search(..) should be a generator.
JPM/TJ: added a test for a possible way to fix unites on cores where the foreignKeySet is not equal to a primaryKey.
JPM/TJ: changed variable names primary, foreign -> result, other
TJ/HM/JPM: Guarding against issue with ComposedQuery with respect to non-unique keys (work in progress).
HM/JPM: adapted rest of Meresco-Lucene to new ComposedQuery interface
HM/JPM: extended ComposedQuery with isSingleCoreQuery method
HM/JPM: back to simply enforcing uniqueKey for resultsFrom core in given match in ComposedQuery