Config setting to nerf corium

For use on servers that have a mainly creative purpose, the setting
enable_corium_griefing=false will prevent corium from flowing far or
unpredictably and from destroying nodes other than water.  All reactor
meltdowns will stay contained.

technic/config.lua

@@ -13,6 +13,7 @@ local defaults = {
 	enable_marble_generation = "true",
 	enable_granite_generation = "true",
 	enable_wind_mill = "false",
+	enable_corium_griefing = "true",
 }
 
 for k, v in pairs(defaults) do

technic/machines/HV/nuclear_reactor.lua

@@ -351,16 +351,19 @@ minetest.register_abm({
 	end,
 })
 
+local griefing = technic.config:get_bool("enable_corium_griefing")
+
 minetest.register_abm({
 	nodenames = {"technic:corium_flowing"},
 	interval = 5,
-	chance = 10,
+	chance = (griefing and 10 or 1),
 	action = function (pos, node)
 		minetest.set_node(pos, {name="technic:chernobylite_block"})
 	end,
 })
 
-minetest.register_abm({
+if griefing then
+	minetest.register_abm({
 		nodenames = { "technic:corium_source", "technic:corium_flowing" },
 		interval = 4,
 		chance = 4,
@@ -377,4 +380,5 @@ minetest.register_abm({
 				end
 			end
 		end,
-})
+	})
+end