edit: Report loading/unloading of planes & land units properly

edit: Report loading/unloading of planes & land units properly

Print a message, send bulletin to owner.  Affects plane keys 's', 'y',
and land unit keys 'S', 'Y'.  The message is necessary to give the
deity a chance to catch unexpected changes, e.g. a player loading a
plane right before the deity edits it.  Watching out for such changes
is especially important with non-interactive edit.

Signed-off-by: Markus Armbruster <armbru@pond.sub.org>