Phase 13 - altitude, heat, scooping and collisions
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All four were missing; the altitude and cabin temperature bars on the dashboard
were nailed to dummy values and nothing could be flown into.

The original looks at the planet on frame 10 of every 32 and at the sun on
frame 20 - which is why those two bars step rather than slide - and both work
on the middle bytes of the coordinates, so both are skipped entirely while
anything is a whole unit away in any axis.  An altitude bar reading full means
no more than "further off than 65536".

Altitude is sixteen times the square root of q - 37, where q is the sum of the
squares of the coordinates in high bytes divided by 256 again.  The planet's
radius is 96 high bytes, which by that same arithmetic is 36, and the original
subtracts 37 rather than 36 so that exactly one radius is fatal too.

Cabin temperature is 285 - q for the sun, so 30 in deep space, 224 at the fuel
scooping threshold and over 255 - fatal - close in.  Scooping takes a tenth of
a light year for every eight of speed.

Scooping needs fuel scoops fitted and the thing below us: you fly over the top
of a canister to take it in.  Anything else within 256 units is a collision.  A
canister holds a random item up to computers, an escape pod holds slaves and a
Thargon counts as alien items.

Measured by putting the planet, the sun and single objects at chosen distances
and calling the routines directly:

  planet 70000    altitude 255   the gauge reads full beyond one unit
  planet 60000    altitude 213
  planet 49152    altitude 166   two radii out
  planet 30000    altitude 65
  planet 24700    DEAD
  planet 24576    DEAD           exactly one radius, as the original intends

  sun 65000       cabin 33       just off the deep-space 30
  sun 40000       cabin 190
  sun 32000       cabin 224      exactly the scooping threshold
  sun 30000       cabin 231      fuel 2.0 -> 2.5 light years at speed 40
  sun 22000       cabin 256      DEAD

  canister below, scoops      taken, "Food" in the hold, no damage
  canister above, scoops      collision, 32 off the shield, not taken
  canister below, no scoops   collision
  escape pod below, scoops    taken as slaves, which is the original's rule
  a Viper at touching range   collision

In the demo the altitude bar now runs 209, 170, 134, 120, 117, 91, 65 on the
way in and back up again as the fighting swings the planet off the axis, and
reads full again after a jump.  Nothing died, which is right: it never flew
straight at the planet for long enough.
