ATIS overhaul by John Denker, adapted to trunk by me.

ATIS overhaul by John Denker, adapted to trunk by me.

8:: AWOS is available at AWOS locations.  (Previously only ATIS was
   implemented.)

 9:: ATIS phraseology now more nearly conforms to international
   standard METAR pattern, and therefore to usual FAA practice.(*)

Items marked with a (*) are fully implemented in the /text/ of the
ATIS message, but the voiced version of the message is degraded by
limitations of the FGFS built-in text-to-speech system.

 10:: ATIS now reports sky condition.(*)

 11:: ATIS now reports multiple layers of clouds, not just the lowest
 layer.(*)

 12:: ATIS now takes field elevation into account when calculating
   sky condition and ceiling.

 13:: ATIS now reports dewpoint.(*)

 14:: ATIS now can handle negative quantities (temperature and dewpoint).(*)

 15:: ATIS can now report report fractional-mile visibility.(*)

 16:: ATIS now uses magnetic (not true) wind directions, as it should.

 17:: ATIS generates correct runway number and suffix (nine right,
   one one left).

 18:: ATIS can be received on nav frequencies, not just comm.

 19:: Nothing bad happens if the same ATIS is tuned up on more than
   one receiver.

 20:: ATIS can be updated at times other than at the top of the hour.

 21:: ATIS listens for an "attention" signal, and responds to changes
   in the weather by issuing a new ATIS message (somewhat like a
   "special observation").

 22:: ATIS volume now responds to radio volume setting.

 23:: Area-related services (i.e. approach radar) are handled
   more-nearly consistently with radio-frequency related services.

 24:: ATIS sequence-letter generation has been fixed.

 25:: ATIS messages are now in the property tree, so they can be read
   e.g. via the http interface.