functions when used in $FG_ROOT/Nasal/*.nas, because it
depends on props.nas being available; no restrictions in
aircraft files, where it will proof most useful
gui.nas: replace inefficient FPS display polling loop with listener
callback
New Node.setValues() method which sets whole property trees from Nasal
data.
A view.nas module, which takes over handling of the X/x zoom keys. It
clamps the FOV to a dynamically calculated maximum corresponding to
typical human visual accuity, and pops up a pretty dialog informing
you of the new FOV.
