Lua 5.2 upgrade [1] for NSE.

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

scripts/smtp-brute.nse

@@ -1,3 +1,10 @@
+local brute = require "brute"
+local coroutine = require "coroutine"
+local creds = require "creds"
+local shortport = require "shortport"
+local smtp = require "smtp"
+local stdnse = require "stdnse"
+
 description = [[
 Performs brute force password auditing against SMTP servers using either LOGIN, PLAIN, CRAM-MD5, DIGEST-MD5 or NTLM authentication.
 ]]
@@ -23,10 +30,6 @@ Performs brute force password auditing against SMTP servers using either LOGIN,
 -- Version 0.1
 -- Created 07/15/2011 - v0.1 - created by Patrik Karlsson <patrik@cqure.net>
 
-require 'creds'
-require 'brute'
-require 'shortport'
-require 'smtp'
 
 author = "Patrik Karlsson"
 license = "Same as Nmap--See http://nmap.org/book/man-legal.html"