Bug 21957: Add a flag to ModBiblio to avoid linking auths if called from linker

Bug 21957: Add a flag to ModBiblio to avoid linking auths if called from linker

To test:
1 - prove -v t/db_dependent/Biblio.t
2 - Set BiblioAddsAuthoorities and AutoCreateAuthorities
3 - Modify a biblio to add a heading with no existing auth record
4 - Ensure the record was created on saving
5 - Ensure that editing works as normal otherwise
6 - Run link_bibs_to_authorities
7 - Ensure results are as expected

Signed-off-by: Michal Denar <black23@gmail.com>
Signed-off-by: Josef Moravec <josef.moravec@gmail.com>
Signed-off-by: Nick Clemens <nick@bywatersolutions.com>