Prevent using a leash while engulfed. If someone wants to supply a
better message, go ahead. I just tried to get the logic straight.
(The new swallowed part is easy; the previous lack of handling for
remembered unseen monsters wasn't quite so easy.)
Applying a leash was always using a move, even if player cancelled
at the prompt to pick an adjacent monster. Now some of the early
exits don't use a move.
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