(pln_airbase_ok, mission_pln_airbase_ok): Oops when plane's carrier is

(pln_airbase_ok, mission_pln_airbase_ok): Oops when plane's carrier is
bad.  Before, the plane was destroyed, and the player got a message.

(pln_airbase_ok, mission_pln_airbase_ok): Oops when plane's base
sector is bad.

(pln_airbase_ok): Oops when the player doesn't own the plane.  Before,
this was checked only for planes on carriers, and the plane was
destroyed, and the player got a misleading message.