Change the DateCalc mode to resolve showing negative times for the next recording.

Change the DateCalc mode to resolve showing negative times for the next recording.

Julian's bug report:

Hello Andrew!

I noticed a bizarre behaviour of mythtv-status: at 9pm, when the next
recording was due at about 6pm the next day, it reported: "Next
Recording In: -3 Hours, -7 Minutes", which is clearly nonsense.  The
attached patch fixes this, and two other bugs:

- if the next recording is in longer than 1 day, it now gives the
  correct time
- if the time is 1 Hour, 1 Minute, it says this correctly (instead of
  saying 1 Hour, 1 Minutes)