surface: Make auto pilot land and take off repeatedly.
surface: Erase a lot of unused codes in Aerial.cpp.

I've kept the codes for future reference, but recent several dozens of
commits proved that they are quite unlikely to be used again.
surface: Renamed Aerial::brk to brake and make it working again.

The old name was too cryptographic, that's why we changed it.
Also, spoiler is distinct concept from brake, so we make it work as
it should.
surface: Fix Aerial::animAI() sets destArrived flag unintentionally.

The bug made the waypoint list in the demo7.nut script to mulfunction.

Also tweaked aerial.nut for more accurate landing.
surface: Multiple A10's in demo7.nut.

Also fixed a bug that Aerial vehicles tries to attack allies.
surface: Add delta-time parameter to aerialLanding to time-integrate.

With this feature, autopilot accuracy would be improved by PID control.
The filter design is still poor, though.
surface: Trying to make autopilot approach logic scripted like landing.

Rudder target is added to returned values of aerialLanding function.

Now we can rapidly prototype approaching autopilot with the method used
in landing AI.

Also a bug is fixed in Entity::sq_pushobj() that could crash the whole
simulation by NULL pointer reference.
Fix lacking const qualifier in SQIntrinsic constructor argument.
Revived Entity getters and setters for intrinsic types from Squirrel.

For details and rationale, refer to the comments added to Entity.cpp in
this commit.
Add estimate_pos implementation into aerialLanding().
surface: Add airbrake motion and gradual effect of brake to A10.
surface: Erase many unused codes in A10-draw.cpp.

Worse, they are duplicated in F15-draw.cpp too.
We certainly won't miss them.
surface: Add navigation lights support to Aerial, specifically A10.
Add typedef name for list of Navlight objects for better virtualization.
surface: Erase unused codes in F15-draw.cpp.

They have been also duplicate of A10-draw.cpp as mentioned in ca93334.
surface: Add navigation lights to F15.
Make accel() method accessible from Squirrel scripts.

The function is really a member of WarField, but defined in CoordSys
for particular reason.
Add slen() member function to Vec3d in Squirrel scripts.

Also enabled debugging information for debug builds.
surface: Make Hellfire missile's homing calculation scripted.

Now we can experiment and tweak the algorithm with the game being kept
running, just like Aerial's case.

The algorithm is just dead copied from C++ source, plus some dynamic
variables per Hellfire instance.  The script provided per-instance
variables are stored in tables referred to with the name "object".
surface: Make Apache derive Aerial to display HUD in cockpit.