Clean up output destinations in march code

Clean up output destinations in march code

lnd_mar(), lnd_sweep() and lnd_mar_one_sector() printed to the current
player, their actor argument, and to land unit owner.
lnd_mar_one_sector()'s use of xyas() looked particularly suspicious:
it passed actor, then printed the result to the current player or land
unit owner.  Fortunately, all three are the same: all callers pass
current player for actor, and land unit owner is the same, since even
deities can't march foreign land units.  Normalize to actor for
consistency.

While there, rename lnd_mess() to lnd_stays().