Bug 11588: fix untranslatable subscription frequency units

To test:

1) cd misc/translator
2) perl translate update xx-YY
3) check that there's no msgid that contains the subscription
   frequencies (day, week, month and year) in
   po/xx-YY-i-staff-t-prog-v-3006000.po (search for
   "BLOCK translate_frequnit")
4) apply patch
5) perl translate update xx-YY
6) check po/xx-YY-i-staff-t-prog-v-3006000.po that it contains the
   msgid for the frequencies. (search for "BLOCK translate_frequnit")

Signed-off-by: Chris Cormack <chris@bigballofwax.co.nz>
Signed-off-by: Kyle M Hall <kyle@bywatersolutions.com>
Signed-off-by: Galen Charlton <gmc@esilibrary.com>