Bug 26641: pass the MARC field as an argument to link_bibs_to_authorities.pl

Bug 26641: pass the MARC field as an argument to link_bibs_to_authorities.pl

When running link_bibs_to_authorities.pl, it could be useful to have
the ability to specify which MARC field the script should operate on.

For example, when you have a catalog where most links are in place,
and you don't want the script to process every MARC field but rather
limit it to a specific MARC field (e.g. 700) because you've observed
that there are many missing links for that particular MARC field.

This patch provides that enhancement.

Test plan:
1) Run the script as follows (preferably in a test DB):

   time link_bibs_to_authorities.pl -v -l --test

   ... and notice how long it takes to complete.

2) Apply the patch.

3) Run the script again, this time providing the MARC field to work on:

   time link_bibs_to_authorities.pl -v -l --test -g=700

   ... and, again, notice how long it takes to complete.

   The 2nd run should run faster than the 1st one.

Signed-off-by: David Cook <dcook@prosentient.com.au>
Signed-off-by: Martin Renvoize <martin.renvoize@ptfs-europe.com>
Signed-off-by: Jonathan Druart <jonathan.druart@bugs.koha-community.org>