baalz hack fixup fix...
I saw a lich in solid wall at one of the spots which gehennom.des
marks with a pool (so that baalz_fixup() can find the two spots that
need post-wallification fixup). I could understand the special level
loader placing a swimming or flying monster there, but don't know
whether it might do that for a lich (which doesn't need to breathe)
so am not sure whether this actually fixes what I observed.
The lich was there for far too long to have been a shapechanger, but
when I went back to the save file it was no longer there, producing
another puzzle.