James Turner:
Trivial patch, but an important milestone:
Convert FGAirport to inherit FGPositioned. This concludes the first phase of the FGPositioned changes, and hopefully the most intrusive ones - adding in the base class. There's lots (and lots) of further work to do on the indexing and querying side, as well as cleaning up the accessors, but that will happen in single source files, or a group of related files at a time.
As a trivial note, this patch does fix a bug where the very last airport in apt.dat would get an invalid type. So for all you people who just love to fly to EHYB (Ypenburg, The Hague), things may work a little more sanely.
I'll intentionally let the dust settle after this patch, so any weird behaviour I may potentially have introduced shows up. Just to re-iterate, so far there should be absolutely no user-visible change in the behaviour of anything - navaids, position init, the route manager, AI flight plans, etc. If there is, please let me know and I'll fix it ASAP.