Bug 8330: Overdue email link contains untranslatable 'Overdue:'

Bug 8330: Overdue email link contains untranslatable 'Overdue:'

The translation scripts don't pick up text from href attributes,
which is what we want, with a small exception for this script.

Patch uses a TT trick to make the Overdue: in the subject
of the mailto: link translatable.

Regression test:
- Make sure you have an overdue item
- Go to Circulation > Overdues
- Verify the [email] link works and a subject
  with 'Overdue: <title>' is generated
- Apply patch and repeat steps

Bonus: Verify the branch name now shows instead of
       the branchcode in the table

To test translatability:
- cd misc/translator
- perl translate update de-DE
- Open file po/de-DE-staff-prog.po
- Search for Overdue:
- Translate string, remove 'fuzzy' marker
- perl translate install de-DE
- Test again, subject should now be translated

Signed-off-by: Nick Clemens <nick@quecheelibrary.org>
Signed-off-by: Tomas Cohen Arazi <tomascohen@unc.edu.ar>