Make actors outside map borders selectable for their owner

PR #5967 only made planes not lose their selection when they strayed
outside the map border. This PR makes it possible to select them when
they already are outside the map.  It also ensures that the selection
decorations are drawn.  Rank designations, however, will disappear when
a unit leaves the map.

Fixes #5651 for real, then.
Make aircraft not waste their missiles by firing from outside the map

Fixes #6001.

This obviously affects Yaks as well as Migs, even though Yaks had no
trouble with attacking from outside the map.