BibIndex: call BibAuthorID for modified person IDs

• When indexing author indexes, in addition to looking at record modification dates, consult also BibAuthorID tables to see whether there have been some claims or other canonical author ID changes, in order to index properly canonical author IDs. (closes #689)

• Amends BibAuthorID's get_recids_affected_since() in order to return list of integers, not list of strings representing integers.