Fix#576
Reported initially by @copperwater for polymorphed monsters:
"observe how the [polymorphed-monster] hovers placidly above the water for
several turns like Wile E. Coyote before it gets a move, realizes it's
above water, and drowns. Ditto for lava."
A comment in the GitHub issue thread by @Tomsod pointed out that a
revived corpse could do the same.
This should set things up for other terrain fallout if discovered or
implemented in the future.
- consume an additional bit in enum mon_terrain_effects (hack.h)
- include the additional bit in TERRAIN_FALLOUT_MASK (monst.h)
- add detection to maybe_set_terrain_effects (mon.c)
- add action to terrain_effects (mon.c)
Implemented by stealing some upper unused mstate bits to avoid
invalidating existing save and bones.