fix github pull request #114 - ant holes in *.des

fix github pull request #114 - ant holes in *.des

Fixes #114

Report and contributed fix described lack of support for room type
"ant hole" in the code that loads special levels (and mentioned that
none of our des files attempted to use that room type so it isn't
noticeable in unmodified version of the game).  The fix overlooked
a couple of other missing room types (leprechaun hall and cockatrice
nest) so I didn't use the pull-request's commit (so not sure what
github's automated updating will make of 'Fixes #114').