Active Directoy support plus other things

Sorry about lumping these all together in one pull request. I didn't commit them to my local repo in a sane way and am too lazy to reorganize it. Updates:

1. Allow authenticated (non-anonymous) bind to LDAP server.
2. Allow choice between 'vanilla' ldap and Active Directory.
3. Add user to multiple groups instead of just the last one they belong to.
4. Small typo correction.

I don't have ready access to a vanilla ldap installation but I tried my best not to break anything. Also, my Python is horrible.

Thanks!