surface: Make Apache derive Aerial to display HUD in cockpit.
surface: Review Hellfire algorithm for better homing capability.
surface: Add queryAmmo interface to Aerial for HUD readout.

Apache, A10 and F15 support the interface to show ammunition count for
currently selected weapon on the HUD.  The weapon name is also virtualized
to allow more flexible overrides than just passing list of weapon names
to drawCockpitHUD().