Lua 5.2 upgrade [1] for NSE.

[1] http://seclists.org/nmap-dev/2012/q2/34

scripts/ftp-brute.nse

@@ -1,3 +1,10 @@
+local brute = require "brute"
+local creds = require "creds"
+local nmap = require "nmap"
+local shortport = require "shortport"
+local stdnse = require "stdnse"
+local string = require "string"
+
 description = [[
 Performs brute force password auditing against FTP servers.
 
@@ -28,10 +35,6 @@ author = "Aleksandar Nikolic"
 license = "Same as Nmap--See http://nmap.org/book/man-legal.html"
 categories = {"intrusive", "brute"}
 
-require 'shortport'
-require 'brute'
-require 'creds'
-
 portrule = shortport.port_or_service(21, "ftp")
 
 local arg_timeout = stdnse.get_script_args(SCRIPT_NAME .. ".timeout") or 5