Merged in my changes from nmap-smb. The primary changes are:

* Updated the way authentication works on smb -- it's significantly cleaner now
* smb-enum-shares.nse gives significantly better output now (it checks if shares are writable)
* Added a script that checks if smbv2 is enabled on a server
* Added smb-psexec, a script for executing commands on a remote Windows server. I also included some default scripts, a compiled .exe to run everything, and a ton of documentation (in the form of NSEDoc)
* Added 'override' parameters to some of the functions in smb.lua, which lets the programmer override any field in an outgoing SMB packet without modifying smb.lua. 
* Lots of random code cleanups in the smb-* scripts/libraries

nselib/data/psexec/backdoor.lua

@@ -0,0 +1,28 @@
+module(... or "backdoor", package.seeall)
+---This config file is designed for adding a backdoor to the system. It has a few
+-- options by default, only one enabled by default. I suggest 
+--
+-- Note that none of these modules are included with Nmap by default. 
+
+-- Any variable in the 'config' table in smb-psexec.nse can be overriden in the
+-- 'overrides' table. Most of them are not really recommended, such as the host,
+-- key, etc.
+overrides = {}
+--overrides.timeout = 40
+
+modules = {}
+local mod
+
+-- TODO: allow the user to specify parameters
+--Note: password can't be longer than 14-characters, otherwise the program pauses for
+-- a response
+mod = {}
+mod.upload           = false
+mod.name             = "Adding a user account: $username/$password" 
+mod.program          = "net"
+mod.args             = "user $username $password /add"
+mod.maxtime          = 2
+mod.noblank          = true
+mod.req_args         = {'username','password'}
+table.insert(modules, mod)
+