Allow defining random-teleport exclusion zones in lua

Adds a new lua command

  des.exclusion({ type = "teleport", region = { x1,y1, x2,y2 } });

which allows defining "exclusion zones" in the level, areas where
random teleports (or falling into the level) will never place the hero.
Does not prevent targeted teleportation into the area.

Breaks saves and bones.

doc/fixes3-7-0.txt

@@ -1228,6 +1228,7 @@ when a werecreature in human form attacked hero, it could transform to critter
 status highlighting for hit points didn't work as intended for up or down HP
 	changes; 'up' rule was used for both, 'down' rule was ignored
 unhide an unseen water monster using a polymorph trap on land
+allow defining random-teleport exclusion zones in lua
 
 
 Fixes to 3.7.0-x General Problems Exposed Via git Repository

doc/lua.adoc

@@ -528,6 +528,18 @@ Example:
  des.engraving({x,y}, "engrave", "Foo");
 
 
+=== exclusion
+
+Exclude an area of the map from being randomly chosen target when
+falling or teleporting into the level.  Multiple exclusions per level are allowed.
+
+* type is one of "teleport", "teleport-up", or "teleport-down".
+
+Example:
+
+ des.exclusion({ type = "teleport", region = { 0,0, 10,5 } });
+
+
 === feature
 
 Create a feature, and set flags for it.