Replace lava with water in castle-3
Add water caves for levels between medusa and castle

These new "medufill" levels are similar to the "hellfill" lava caves,
but with water and less evil monsters.  Also, there's no chance of
rooms-and-corridor levels between medusa and castle anymore.
Guarantee a wand of cancellation in castle chest

Getting the wand of wishing at the castle is when players begin their
stash work, so giving them a wand of cancellation should give them a way
to blank potions and scrolls without having to haul them to the nearest
source of water to their stash.