MDL-9399 auth/ldap: Add NTLM SSO pages

MDL-9399 auth/ldap: Add NTLM SSO pages

These pages control the process of attempting an NTLM SSO login
safely. This is very draft and needs real-world testing and polish.

And string localisation too ;-)

  * If NTLM SSO is enabled, and the user's IP addr is in the right
    subnet, the loginpage_hook() of auth/ldap redirects to
    ntlmsso_attempt.php

  * ntlmsso_attempt.php will display a "redirect" msg with an img tag
    pointing to ntlmsso_magic.php, a 3s wait, and a redirect to
    ntlmsso_finish.php

  * ntlmsso_magic.php should be configured to have "Integrated
    Windows Authentication". If it does, it will serve a spacer gif
    and call ntlmsso_magic()

  * ntlmsso_finish.php calls ntlmsso_finish() to complete the SSO
    and handles failures.