database changes

 - changed tables to start with 3rd_ instead of eq_
 - added prospective flag to 3rd_elder table
 - added visit_type, companion1, companion2 fields to 3rd_visit table
 - changed 3rd_ppi table to 3rd_interview
 - "converted" eqpresppi field to interview_type (enumeration) in 3rd_interview table
 - changed ppi field to interview in 3rd_interview table

more changes

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