Lua 5.2 upgrade [1] for NSE.

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

scripts/http-waf-detect.nse

@@ -1,3 +1,9 @@
+local http = require "http"
+local shortport = require "shortport"
+local stdnse = require "stdnse"
+local string = require "string"
+local table = require "table"
+
 description = [[
 Attempts to determine whether a web server is protected by an IPS (Intrusion Prevention System), IDS (Intrusion Detection System) or WAF (Web Application Firewall) by probing the web server with malicious payloads and detecting changes in the response code and body.
 
@@ -44,9 +50,6 @@ author = "Paulino Calderon"
 license = "Same as Nmap--See http://nmap.org/book/man-legal.html"
 categories = {"discovery", "intrusive"}
 
-require "http"
-require "shortport"
-require "url"
 
 portrule = shortport.http