added io library isolation so logic functions cant access the io functions

sim/iosafe.lua

@@ -0,0 +1,22 @@
+
+assert(not io.safe, "re-execution of iosafe")
+
+local iosafe = io
+_G.io = {safe = true}
+local requiresafe = require
+_G.require = nil
+
+local savedir = OPT_SAVE_DIR
+
+function io.open(fn, mode)
+	fn = fn:gsub("\\", "/")
+	assert(not fn:find("[^a-zA-Z0-9%._ ]"), "illegal character in file name \""..fn.."\"")
+	assert(not fn:find("%.%."), "illegal updir in file name \""..fn.."\"")
+	fn = fn:gsub("^/", "")
+	
+	fn = savedir.."/"..fn
+	
+	print("access file \""..fn.."\"")
+	
+	return iosafe.open(fn, mode)
+end