Follow user preference in calendar diagnostics

Follow user preference in calendar diagnostics

Respect text-quoting-style preference in diagnostic formats by
using curved quotes (which are translated as per text-quoting-style)
instead of grave accent and apostrophe (which are not).
* lisp/calendar/appt.el (appt-display-message):
* lisp/calendar/diary-lib.el (diary-check-diary-file)
(diary-mail-entries, diary-from-outlook):
* lisp/calendar/icalendar.el (icalendar-export-region)
(icalendar--convert-float-to-ical)
(icalendar--convert-date-to-ical)
(icalendar--convert-ical-to-diary)
(icalendar--convert-recurring-to-diary)
(icalendar--add-diary-entry):
* lisp/calendar/time-date.el (format-seconds):
* lisp/calendar/timeclock.el (timeclock-mode-line-display)
(timeclock-make-hours-explicit):
* lisp/calendar/todo-mode.el (todo-prefix, todo-delete-category)
(todo-item-mark, todo-check-format)
(todo-insert-item--next-param, todo-edit-item--next-key)
(todo-mode):
Use curved quotes in diagnostic format strings.
* lisp/calendar/icalendar.el (icalendar-import-format-sample):
* test/automated/icalendar-tests.el (icalendar--import-format-sample):
Just use straight quoting for simple test case.