Bug 11492: Keep routing notes when receiving next serial

Bug 11492: Keep routing notes when receiving next serial

This patch ensures the routing notes are carried over when generating
the next serial.

To test:
1) Create a routing list for a subscription
2) Add a borrower and a note to the routing list
3) Generate the next serial (serials-collection.pl)
4) Edit the routing list to see the notes
5) Note that the notes have disappeared
6) Apply patch
7) Edit the routing list, add a note
8) Generate the next serial
9) Edit the routing list and confirm the note is still there
10) Confirm you are still able to edit serials (serials-edit.pl) and
routing notes stay

Sponsored-by: Plant and Food Research Limited
Signed-off-by: Nazlı Çetin <nazli@devinim.com.tr>
Signed-off-by: Liz Rea <wizzyrea@gmail.com>
Signed-off-by: Marcel de Rooy <m.de.rooy@rijksmuseum.nl>
Signed-off-by: Martin Renvoize <martin.renvoize@ptfs-europe.com>