[mythtv] FIX "do not autoexpire" Flag made persistent

[Chris Pinkham]

> What if we just inverted the flag so that it indicates "Keep this until 
> I delete it".  Then it's just a matter of a dbCheck update and some UI 
> text for the existing installations.

If all people want "Preserve" to mean is that the system won't delete a
recording, but that the user can, then this might work.  If "Preserve"
means that the user (or their kids) can't accidentally delete a recording,
then this won't.

I could go for either definition since I don't have any kids right now. :)

-- 

Chris