Bug 19327: Typo in UNIMARC field 128a plugin

Bug 19327: Typo in UNIMARC field 128a plugin

This patch corrects some incorrect information in the UNIMARC plugin for
tag 128$a. The value for "partsong" should be "pt#"

To test you do not need a UNIMARC installation. Apply the patch and go
to Administration -> MARC frameworks and Actions -> MARC structure for
one of your frameworks.

- Edit subfields for a tag, e.g. 245. This is only for testing purposes
  so it doesn't have to be any particular tag.
- Change the options for one of the subfields, e.g. $a. Under "Other
  options (choose one), set "Plugin" to "unimarc_field_128a.pl"
- Save changes.
- Open a bibliographic record for editing using the framework you
  modified.
- Click the plugin link next to the subfield you modified, e.c.
  245$a.
- This should trigger the "UNIMARC field 128a builder" popup window.
- Select "partsong" in the dropdown. Save.
- In the MARC editor, the field you modified should contain the
  value "pt#"
- Trigger the popup window again and click "Save" without making
  changes.
- The value in the MARC editor should be the same.

Signed-off-by: David Nind <david@davidnind.com>
Signed-off-by: Katrin Fischer <katrin.fischer.83@web.de>
Signed-off-by: Jonathan Druart <jonathan.druart@bugs.koha-community.org>