Index corporate author by relator code as well as relator text

[Dan Scott]

* Evergreen rel_2_3 / master

The existing stock index for corporate authors only kicks in if the 710 subfield 'e' == 'creator', but relator codes (in subfield '4') are by many accounts a preferred mode of identifying the relationship of an added entry. Thus, add '4' == ('aut' or 'cre') to the criteria for indexing a corporate author.

Please see user/dbs/corporate_author in working for a branch with a simple change to the config.metabib_field stock definition and associated upgrade script.

[Ben Shum (bshum)]

Works for me. Thanks Dan.

Fix in master and rel_2_3.