Bug 20478: Have the cronjob script advance_notices.pl send digest messages per branch.

Bug 20478: Have the cronjob script advance_notices.pl send digest messages per branch.

Desired behavior of the script advance_notices.pl is that the sender
address on the notice message is that of the branch of the issues in
question.  Thus, the solution is to generate digest messages per
branch.

To test:
1) Inspect unit test in t/db_dependent/cronjobs/advance_notices_digest.t and note that:
   - There are three libraries
   - There is a borrower
   - The borrower is registered at library1
   - The borrower has message preference wants_digest set to 1
   - The borrower has message preference days_in_advance set to 1
   - The content of the letter PREDUEDGST is '<<count>> <<branches.branchname>>'
   - There are three items
   - There is one issue per item
   - There is one issues at library2
   - There are two issues at library3
   - The date_due of the issues are set to tomorrow
   - For the default case (no -digest-per-message)
      - It is asserted that there is one message in the message queue after running the script
      - It is asserted that there are three items in the message.
      - It is asserted that the branchname is that of the borrower's home library.
   - For the case where -digest-per-message is enabled
      - It is asserted that there are two messages in the message queue after running the script
      - It is asserted that the item count of the message corresponding to library2 is 1
      - It is asserted that the item count of the message corresponding to library3 is 2
      - It is asserted that the branchnames are correct.
2) Run unit test: prove t/db_dependent/cronjobs/advance_notices_digest.t

Sponsored-By: Bibliotek Mellansjö, which is a cooperation between
Sponsored-By: Gullspångs kommunbibliotek
Sponsored-By: Hjo stadsbibliotek
Sponsored-By: Karlsborgs bibliotek
Sponsored-By: Mariestads stadsbibliotek
Sponsored-By: Skövde stadsbibliotek
Sponsored-By: Tibro bibliotek
Sponsored-By: Tidaholms stadsbibliotek
Sponsored-By: Töreboda kommunbibliotek
Signed-off-by: Andreas Jonsson <andreas.jonsson@kreablo.se>
Signed-off-by: Magnus Enger <magnus@libriotech.no>
Adding the --digest-per-branch switch turns the digest into one digest per
library. I think it makes perfect sense to keep the default behaviour
and hide this new functionality behind a command line switch.
Signed-off-by: Martin Renvoize <martin.renvoize@ptfs-europe.com>
Signed-off-by: Nick Clemens <nick@bywatersolutions.com>