(pln_oneway_to_carrier_ok): New.

(pln_oneway_to_carrier_ok): New.
(fly, reco): Use it to prevent flying to a carrier that doesn't have
space for the planes.  Previously, planes that did this were
teleported home, which could be abused.

(fly): Fail if pln_sel() comes up empty, just like the other commands
to fly planes.