Relocate the start-up position to a plausible hold-short position
when MP is active and a runway start is requested. This does not (yet)
use ground-net data to identify a real hold-short position.
Remove uses of .str(), .c_str() and some other methods of SGPath.
Pass SGPath directly where possible, or explicitly convert to the
appropriate 8-bit encoding.
Make position finalisation happen in the same phase as scenery load, i.e as a task during the main loop, instead of during the init loop. This is compatible with the existing reset logic. Unfortunately more work is needed; the environment code doesn't update the local station quickly enough on reset. (Fixing that is next!)
Modify startup sequence, so position can be modified late in the startup process, right before the scenery load starts. This allows two ugly hacks to move to a permanent, less hacky location. If other position init modes required similar late evaluation in the future, this can be accommodated now.
This is a somewhat high-risk change - I've tested both carrier starts and runway-selection based on realwx METAR, but please look out for other position-init issues and test before / after this patch.
In preparation for caching the groundnet in the NavCache, make taxi-nodes and parkings inherit from FGPositioned. As part of this, make them heap (as opposed to value) classes, disable their copy-constructors, remove many mutating operations, and give them real constructors.
Cache the parsed navigation and airport data in a binary file to reduce
startup times and memory consumption (since only referenced FGPositioned
elements are held in memory).
Data will be reimported when the mod-time of any input file is changed.
If a global file is changed (nav.dat, awy.dat, apt.dat, etc), the cache
will be completely rebuilt, which takes approximately 30 seconds on
moderate hardware. (Future work may reduce this).
Separate other init functions from position init, since they are unrelated, and made fg_init.cxx very complex. Next step will be brining some sanity to the position init logic :)
