More interesting Gehennom levels

Instead of just plain old boring mazes, spice up Gehennom by
occasionally adding lava, iron bars, or even mines-style levels
(with lava, of course).

Of the fixed Gehennom levels, only Asmodeus' lair has been changed
to add some random lava pools.

Also some lua fixes and changes:
- Fixed a selection negation bounding box being wrong.
- Fixed a selection negated and ORed returning wrong results.
- des.map now returns a selection of the map grids it touched.
- When using des.map contents-function the commands following the
  map are not relative to it.

sys/unix/Makefile.top

@@ -97,7 +97,7 @@ SPEC_LEVS = asmodeus.lua baalz.lua bigrm-*.lua castle.lua fakewiz?.lua \
 	juiblex.lua knox.lua medusa-?.lua minend-?.lua minefill.lua \
 	minetn-?.lua oracle.lua orcus.lua sanctum.lua soko?-?.lua \
 	tower?.lua valley.lua wizard?.lua nhcore.lua nhlib.lua themerms.lua \
-	astral.lua air.lua earth.lua fire.lua water.lua
+	astral.lua air.lua earth.lua fire.lua water.lua hellfill.lua
 QUEST_LEVS = ???-goal.lua ???-fil?.lua ???-loca.lua ???-strt.lua
 
 DATNODLB = $(VARDATND) license symbols