Do not handle NTLM authentication requests

[phaas]

Avoid handling NTLM authentication requests in the SpnegoAuthenticationProcessingFilter, since the payload is not a valid Spnego token.

These tokens are currently treated as a SpNego token and passed to the GSSAPI, which throws an exception GSSException: Defective token detected (Mechanism level: GSSHeader did not find the right tag).

Depending on the error handler, IE may think that it successfully authenticated via NTLM and/or continue to sent NTLM tokens on subsequent requests.
IE also likes to preemtively send NTLM tokens when posting forms (i.e. instead of posting a FORM with the actual data, it sends a zero-byte POST with an NTLM header, expects the server to issue an NTLM challenge and will ultimately retry the POST once it's confident that it's authorized.
This breaks badly when servers don't actually implement NTLM authentication.

[rwinch]

Thanks for the PR! This is now merged into master