Add ActionQueue priority system

This makes effectors nearer to the source of the action (the receptor) update first.

This defines behaviour for this piston circuit: http://i.imgur.com/9Pp2Mzb.png
And defines, that this memory circuit does not work from this direction: http://i.imgur.com/jJn0aFh.png
But it will work when using the switch from the other side: http://i.imgur.com/nvw0oZB.png

Only if two effectors have the same distance, there is nothing we can do about it, behaviour is not defined.
"Distance" is determined by the stack size of recursions in turnon / turnoff.
Priorities are between 0 (lowest) and 1 (highest).

mesecons/util.lua

@@ -169,6 +169,7 @@ function mesecon:cmpSpecial(r1, r2)
 end
 
 function mesecon:tablecopy(table) -- deep table copy
+	if type(table) ~= "table" then return table end -- no need to copy
 	local newtable = {}
 
 	for idx, item in pairs(table) do