retreat: Don't retreat the current player's ships or land units
The retreat code happily retreats anything, without considering who
owns it. It reports retreat to the owner by bulletin, even when the
owner is the current player.
Commands shouldn't report to the current player by bulletin, they
should print directly. Fixable. However, your ships and land units
retreating from your own actions makes little sense. Suppress it.
Signed-off-by: Markus Armbruster <armbru@pond.sub.org>