shp_sweep() and lnd_sweep() print only a couple of "Sweep...".
Sometimes, the sector isn't obvious, e.g. when you march multiple
sectors in one go, sweeping along the way.
Print "Approaching minefield at X,Y..." right before the first sweep
in a sector.
Note that retreat.c duplicates the sweeping code. Retreating ships
report sweeping with coordinates since commit dcd0794, v4.2.21.
Retreating land units still sweep silently. Left for another day.
Signed-off-by: Markus Armbruster <armbru@pond.sub.org>
Markus Armbruster
c8ead1ec33