Bug 8334 - Authority UNIMARC 100 field plugin

Bug 8334 - Authority UNIMARC 100 field plugin

This patch adds a plugin for field 100 of UNIMARC
authorities.

To test on a UNIMARC site:
1) Apply the patch
2) Edit some authority framework, field 100
3) Link subfield 'a' to unimarc_field_100_authorities.pl
plugin, save
4) Edit or add auth record, click on '...' to bring plugin
5) Modify field 100a
6) Save record

Thanks to Bernardo Gonzalez Kriegel <bgkriegel@gmail.com> for
converting Vitor's original patch to a Git patch and doing
some tidying.

Signed-off-by: Mathieu Saby <mathieu.saby@univ-rennes2.fr>
Signed-off-by: Stephane Delaye <stephane.delaye@biblibre.com>
Signed-off-by: Jonathan Druart <jonathan.druart@biblibre.com>
Signed-off-by: Galen Charlton <gmc@esilibrary.com>