Improve the LuaController

Changes:
  * Stops code after a certain number of instructions.
  * Allows functions, due to instruction counting.
  * Allows loops and goto with non-JIT Lua (LuaJIT doesn't count looping as an instruction, allowing infinite loops), due to instruction counting.
  * Removes string matching functions as they can be slow.
  * Adds some safe functions.
  * Limits the amount of printing that can be done (to prevent console flooding).
  * Code cleanup.
  * More...

mesecons/legacy.lua

@@ -1,18 +1,13 @@
-minetest.swap_node = minetest.swap_node or function(pos, node)
-	local data = minetest.get_meta(pos):to_table()
-	minetest.add_node(pos, node)
-	minetest.get_meta(pos):from_table(data)
-end
+local rules = {
+	a = {x = -1, y = 0, z =  0, name="A"},
+	b = {x =  0, y = 0, z =  1, name="B"},
+	c = {x =  1, y = 0, z =  0, name="C"},
+	d = {x =  0, y = 0, z = -1, name="D"},
+}
 
-local rules = {}
-rules.a = {x = -1, y = 0, z =  0, name="A"}
-rules.b = {x =  0, y = 0, z =  1, name="B"}
-rules.c = {x =  1, y = 0, z =  0, name="C"}
-rules.d = {x =  0, y = 0, z = -1, name="D"}
-
-function legacy_update_ports(pos)
+function mesecon.legacy_update_ports(pos)
 	local meta = minetest.get_meta(pos)
-	L = {
+	local ports = {
 		a = mesecon:is_power_on(mesecon:addPosRule(pos, rules.a),
 			mesecon:invertRule(rules.a)) and
 			mesecon:rules_link(mesecon:addPosRule(pos, rules.a), pos),
@@ -26,7 +21,12 @@ function legacy_update_ports(pos)
 			mesecon:invertRule(rules.d)) and
 			mesecon:rules_link(mesecon:addPosRule(pos, rules.d), pos),
 	}
-	local n = (L.a and 1 or 0) + (L.b and 2 or 0) + (L.c and 4 or 0) + (L.d and 8 or 0) + 1
+	local n =
+		(ports.a and 1 or 0) +
+		(ports.b and 2 or 0) +
+		(ports.c and 4 or 0) +
+		(ports.d and 8 or 0) + 1
 	meta:set_int("real_portstates", n)
-	return L
+	return ports
 end
+