+ * Retrieve from prev-next cache.
+ *
+ * This function is used from a variety of merge related functions, although
+ * it would probably be good to converge on calling CRM_Dedupe_Merger::getDuplicatePairs.
+ *
+ * We seem to currently be storing stats in this table too & they might make more sense in
+ * the main cache table.
+ *
+ * @param string $cacheKey
+ * @param string $join
+ * @param string $whereClause