Expose core random number functions to lua

Expose nh.rn2() and nh.random() to lua.
Add a math.random() compatibility shim to nhlib.lua

dat/nhlib.lua

@@ -1,5 +1,16 @@
 
-math.randomseed( os.time() )
+-- compatibility shim
+math.random = function(...)
+   local arg = {...};
+   if (#arg == 1) then
+      return 1 + nh.rn2(arg[1]);
+   elseif (#arg == 2) then
+      return nh.random(arg[1], arg[2] + 1 - arg[1]);
+   else
+      -- we don't support reals
+      error("NetHack math.random requires at least one parameter");
+   end
+end
 
 function shuffle(list)
    for i = #list, 2, -1 do