Fix undervater being of filler material. Fix stone layer under oceans.

rocks/ign.lua

@@ -60,7 +60,7 @@ rocks.register_igneous_stratus=reg
  minetest.register_ore({
   ore="rocks:granite", wherein="default:stone",
   ore_type="scatter", clust_scarcity=3^3, clust_num_ores=6^3, clust_size=6,
-  height_min=-31000, height_max=-49,
+  height_min=-31000, height_max=-31,
  })
 
 -- continental (granite): diorite and gabbro

rocks/sed.lua

@@ -117,7 +117,7 @@ do
    -- to fix weirid sand layers underground
    def.node_shore_top=def.node_top
    def.node_shore_filler=def.node_filler
-   def.node_underwater=def.node_filler
+   def.node_underwater=def.node_top
   end
   -- and call the saved method to actually do the registration
   old_register_biome(def)