Warn/fallback if calculated (latitude, longitude) is (0, 0)

[Edward Z. Yang]

Under certain circumstances, the gnome-clock applet will return bogus results for latitude and longitude, even though timezone is configured correctly: usually, these bogus results are just (0.0000, 0.0000), which Redshift will happily interpret as a real latitude and longitude. If you live on the east coast of the US, this means Redshift will get the calculations backwards (night when day, etc.)

There are a few things that Redshift could do to make it easier to figure out when this has happened:

- Output a warning if it calculates that your latitude and longitude are 0,0. Fortunately, this location is in the middle of the South Atlantic Ocean, so it is supremely unlikely you'll step on anyone's toes.
- Automatically fall back to timezone for a non-summer/winter aware calculation.
- Automatically fall back to an alternative method of calculating latitude/longitude
- In verbose mode, print the latitude/longitude you think the user is at, and what method you got it from!

I'd be happy to supply a patch, tell me what you want to do.