Bug 21958: Fix bibliographic record field comparison with authority

Bug 21958: Fix bibliographic record field comparison with authority

This makes the comparison between bibliographic field and authority field more robust and per subfield. This makes the comparison not consider the same e.g. the following fields:

$a Test User
$a Test $b User

The actual issue cannot be as easily reproduced with the patches for bug 21826 applied, but here's a test plan anyway:

1. Make sure tests pass (especially t/db_dependent/AuthoritiesMarc*)
2. Make sure authority linking still works properly
3. Make sure authority and biblio frameworks allow subfield i
4. Make sure that even if you add subfield i to 700 in biblio, authority link is kept the same
5. Make sure that even if you add subfield i to the authority record, the authority link is kept the same

Signed-off-by: Frank Hansen <frank.hansen@ub.lu.se>
Signed-off-by: Martin Renvoize <martin.renvoize@ptfs-europe.com>
Signed-off-by: Jonathan Druart <jonathan.druart@bugs.koha-community.org>