Warning only if ISSN in WorldCat and not local data, or in local and not WorldCat

[nflorin]

So long as the one extant ISSN matches the ISSN database, then an ISSN in one of the local data or the WorldCat MARC and not the other should trigger a warning but not an error.

[nflorin]

I think the way to do this is to:

1. Keep local_issn_does_not_match_issn_db but make it non-fatal by default.
2. Add a non-fatal wc_issn_does_not_match_issn_db.
3. Convert the nebulous issn_mismatch to something that boils down to "neither the local nor the WorldCat ISSN matches the ISSN database".

So something like:

if local_issn and wc_issn_a:
    if local_issn_does_not_match_issn_db and wc_issn_does_not_match_issn_db:
        issn_mismatch = '1'
elif local_issn and local_issn_does_not_match_issn_db:
     issn_mismatch = '1'
elif wc_issn_a and wc_issn_does_not_match_issn_db:
    issn_mismatch = '1'

The holy grail would be a way to match against the ISSN database by title. That would let us know when there's an ISSN in the database even if it doesn't appear in the local or WorldCat data. But that's a ways off if it ever happens.

[nflorin]

This is done.

• issn_mismatch was renamed to no_issn_matches_issn_db and is by default a fatal error.
• I added output for wc_issn_does_not_match_issn_db.
• wc_issn_does_not_match_issn_db, local_issn_does_not_match_issn_db, and local_issn_does_not_match_wc_issn_a are all optional fatal errors that by default are only warnings.