I've done som more work on the gps instrument.
- You can now input airport-, nav- or fix-ID to select a waypoint.
- You have to specify either "airport", "nav" or "fix" in the waypoint-type
property (some fixes and navs have identical IDs).
- Formatted the time to waypoint output.
- Cleaned up and changed some propery names (wp-heading -> wp-bearing).
- I've also added a name member to the FGNav class so that the gps instrument
can get the name of the nav.
- Changed the airport name parsing in simple.cxx.
places now use sgCartToGeod() instead of rolling their own
approximation. And YASim is now using exactly the same 3D coordinate
system as the rest of FlightGear is.
