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.

doc/fixes3-7-0.txt

@@ -1081,6 +1081,7 @@ prevent paralyzed hero from helping nymph or succubus remove worn armor
 when identifying items via menu and more than one pass is needed (so when
 	identifying 3 items and player only picks 1, for instance), issue
 	--More-- because the next menu might cover up the ID message(s)
+slightly more interesting Gehennom filler levels
 
 
 Fixes to 3.7.0-x Problems that Were Exposed Via git Repository