(diary-check-diary-file): New function.

(diary-check-diary-file): New function.
(diary, view-diary-entries, show-all-diary-entries)
(mark-diary-entries): Use it.
(view-other-diary-entries): Doc fix.  Use `prefix-numeric-value'.
(diary-syntax-table, diary-attrtype-convert, diary-mail-days): Doc fix.
(diary-modified, d-file): No need to defvar (for compiler).
(list-diary-entries): No need for `let*' so use `let'.
(simple-diary-display): Use `diary-file' directly rather than
inheriting `d-file' from `list-diary-entries' caller.
(make-fancy-diary-buffer, show-all-diary-entries): `mode-line-format'
already buffer-local.
(diary-mail-addr): Set to the empty string (rather than nil) if
undefined, as per `user-mail-address'.
(diary-mail-entries): Doc fix.  Error if `diary-mail-address' unset.
(mark-sexp-diary-entries): Don't regexp-quote sexp-mark twice.
Remove an un-needed `if'.
(list-sexp-diary-entries): Remove local vars mark and s-entry, and
use `let' rather than `let*'.
(diary-date, insert-monthly-diary-entry)
(insert-yearly-diary-entry, insert-anniversary-diary-entry)
(insert-block-diary-entry, insert-cyclic-diary-entry)
(font-lock-diary-date-forms): No need for `let*' so use `let'.
(make-diary-entry): Doc fix.  Use `or' rather than `if'.
(diary-font-lock-keywords): Use `when'.  `cal-islam' is required
feature, not `cal-islamic'.
`calendar-islamic-month-name-array-leap-year' does not exist - use
`calendar-islamic-month-name-array'.