stand/lua: Remove a magic number/string (not a trivial literal)

We'll arbitrarily use KEYSTR_ for string representations of non-trivial
characters.

stand/lua/core.lua

@@ -32,6 +32,8 @@ local core = {};
 core.KEY_ENTER = 13;
 core.KEY_BACKSPACE = 127;
 
+core.KEYSTR_ESCAPE = "\027";
+
 function core.setVerbose(b)
 	if (b == nil) then
 		b = not core.verbose;

stand/lua/menu.lua

@@ -161,7 +161,7 @@ menu.welcome = {
 		name = function()
 			return color.highlight("Esc").."ape to loader prompt";
 		end,
-		alias = {"\027"}
+		alias = {core.KEYSTR_ESCAPE}
 	},
 
 	-- reboot