Use 10.5+ notifications for locale/time zone changes.

Also fix method naming.
Update comment to indicate the current state of Perl versions.
Remove "on" between time and date.

This didn't work with natural language dates of the form "in 2 days", etc; read like a sentence, it would have been "on in 2 days".

Also fix the key view loop in the snooze until sheet.
Replace use of obsolete Date::Manip TZ config variable.