Islamic date diary entries must be prefaced by `islamic-diary-entry-symbol'
\(normally an `I'). The same `diary-date-forms' govern the style
of the Islamic calendar entries, except that the Islamic month
-names must be spelled in full. The Islamic months are numbered
+names cannot be abbreviated. The Islamic months are numbered
from 1 to 12 with Muharram being 1 and 12 being Dhu al-Hijjah.
If an Islamic date diary entry begins with `diary-nonmarking-symbol',
the entry will appear in the diary listing, but will not be