Use new pln_is_in_orbit() when we want to test for orbit specifically,
and test PLN_LAUNCHED when we want to test whether the plane not
sitting in the sector (because it is flying). This distinction is
pointless at this time, because the only way PLN_LAUNCHED gets set is
when a satellite goes into orbit. It will become useful in a later
commit, which will use PLN_LAUNCHED to mark flying planes.
other. Ensure headers in include/ can be included in any order
(except for econfig-spec.h, which is special). New header types.h to
help avoid inclusion cycles. Sort include directives. Remove some
superflous includes.
