created a new class, FGViewPoint (declared in viewer.hxx) that holds a
single position in FlightGear coordinates, and have used it to factor
a lot of the common code out of viewer_lookat.cxx and viewer_rph.cxx.
I don't know whether this new class will stay or not; it might just be
a temporary step, or it might end up taking over much of the current
viewer functionality. It would be a bad idea to code against it right
now.
fix startup sequence problems where we initialize the FDM before we know
the desired starting altitude.
These changes delay fdm initialization until the local tile has been loaded
and we can do a real intersection and find the true ground elevation.
In order to do this, I depend more on the property manager as glue, rather
than the FGInterface.
There are some glitches still when switching to a new airport or reseting
the sim. I will work on addressing these, but I need to commit the changes
so far to keep in sync with other developers.
