Planes now spot ships and land units only when flying recon or sweep,
and along all of their flight path instead of just the target sector.
It still takes a spy plane to identify ships and land units.
Before, non-spy planes spotted ships and land units only in the target
sector, regardless of type of sortie, once for all ships and land
units, in ac_encounter(), once for ships firing flak, in
ac_shipflak(), and once for land units firing flak, in ac_landflak().
Remove all that.