limit redstone distance by checking for players

This should probably be implemented by having redstone signals
lose strength like in mc. This just prevents redstone action
further than 40 nodes from each player.

mods/ITEMS/REDSTONE/mesecons/util.lua

@@ -346,8 +346,16 @@ function mesecon.vm_abort()
 	vm_cache = nil
 end
 
+local function is_player_close(pos)
+	for k,p in pairs(minetest.get_connected_players()) do
+		local d=vector.distance(pos,p:get_pos())
+		if d < 40 then return true end
+	end
+end
+
 -- Gets the cache entry covering a position, populating it if necessary.
 local function vm_get_or_create_entry(pos)
+	if not is_player_close(pos) then return end
 	local hash = hash_blockpos(pos)
 	local tbl = vm_cache[hash]
 	if not tbl then
@@ -364,6 +372,7 @@ end
 -- transaction.
 function mesecon.vm_get_node(pos)
 	local tbl = vm_get_or_create_entry(pos)
+	if not tbl then return end
 	local index = tbl.va:indexp(pos)
 	local node_value = tbl.data[index]
 	if node_value == minetest.CONTENT_IGNORE then
@@ -380,6 +389,7 @@ end
 -- Existing param1, param2, and metadata are left alone.
 function mesecon.vm_swap_node(pos, name)
 	local tbl = vm_get_or_create_entry(pos)
+	if not tbl then return end
 	local index = tbl.va:indexp(pos)
 	tbl.data[index] = minetest.get_content_id(name)
 	tbl.dirty = true
@@ -393,6 +403,7 @@ end
 --
 -- Inside a VM transaction, the transaction’s VM cache is used.
 function mesecon.get_node_force(pos)
+	if not is_player_close(pos) then return end
 	if vm_cache then
 		return mesecon.vm_get_node(pos)
 	else
@@ -424,6 +435,7 @@ function mesecon.swap_node_force(pos, name)
 		-- This serves to both ensure the mapblock is loaded and also hand us
 		-- the old node table so we can preserve param2.
 		local node = mesecon.get_node_force(pos)
+		if not node then return end
 		node.name = name
 		minetest.swap_node(pos, node)
 	end