cavestuff ground content

Pebbles are given to mapgen as decorations, so they have
been left as ground content.
The stalactites are not ground content

cavestuff/nodes.lua

@@ -78,6 +78,7 @@ minetest.register_node("cavestuff:stalactite_1",{
 	drawtype="nodebox",
 	tiles = {"undergrowth_pebble.png"},
 	groups = {cracky=3,attached_node=1},
+	is_ground_content = false,
 	description = S("Stalactite"),
 	paramtype = "light",
 	paramtype2 = "wallmounted",
@@ -124,6 +125,7 @@ minetest.register_node("cavestuff:stalactite_2",{
 	drawtype="nodebox",
 	tiles = {"undergrowth_pebble.png"},
 	groups = {cracky=3,attached_node=1,not_in_creative_inventory=1},
+	is_ground_content = false,
 	drop = "cavestuff:stalactite_1",
 	paramtype = "light",
 	paramtype2 = "wallmounted",
@@ -142,6 +144,7 @@ minetest.register_node("cavestuff:stalactite_3",{
 	drawtype="nodebox",
 	tiles = {"undergrowth_pebble.png"},
 	groups = {cracky=3,attached_node=1,not_in_creative_inventory=1},
+	is_ground_content = false,
 	drop = "cavestuff:stalactite_1",
 	paramtype = "light",
 	paramtype2 = "wallmounted",