Cindy: Fixing trigger for next wave

A next wave was triggered when only one Yeti was alive. This means when
during the 10th wave only one last Yeti was alive, then every 5 seconds
$@FIGHT_YETI_WAVE was incremented. If the last Yeti was not killed within
one minute, then wave 22 was reached and the deadly Yeti spawn happend.

This bug fix also resolves the timing problem mentioned in the comment.
Cindy: Spawning one more Yeti at each wave

With the last bug fix the quest got a bit easier. This commit
makes it a bit more difficult again. If the players manage to
kill all Yetis before the round timer triggers the next wave,
then the maximum number of Yetis alive is the same as in the past.

For the benefit of the hero's companions Cindy now announces the 0th
wave publically.
Run 'make maps' to update the spawn time of the Jack-O on 018-1.