These variant present "Do not show again" checkbox.
If checked and the Opt dialog is invoked again with the same opt_id, then the same value as the last time is returned withou showing the dialog.
Opt1 does this only if user selects button that returns 1 (e.g. Yes) - this is because sometimes it would be pretty confusing that some operation with "do you want to continue" prompt would be blocked forever...
If opt_id is not specified (NULL), it is created by hashing the message text.