AD group membership authentication

Integrated changes from forum thread http://forum.pfsense.org/index.php/topic,62562.msg342025.html#msg342025 - auth.inc.patched.txt
I think I have got just the changes related to this functionality! The other differences with the 2.0.3 code seemed to all be real changes in 2.0.n that came after the "patched.txt" file.
Have tested that the syntax is OK. Cannot test the functionality.