Make NTLM SSP support optional (fixes #52)

[devurandom]

No description provided.

[simo5]

I think all we need really is to change gss_mech_ntlmssp to be of type gss_OID (a pointer) and define it to GSS_C_NO_OID when gssapi/gssapi_ntlmssp.h is not available.

Then change a couple of callers to make sure they do not balk when it is NULL.

[devurandom]

Second try. Be warned: I couldn't test it, yet.

[simo5]

Ah I did not see you proposed a new fix, so I opened #54
note that your code fails to compile if you do have gssapi_nlmssp.h

Can you test #54 ?
If it works for you I'll add a comment about it being co-authored by you and push that one.

[devurandom]

Oups, yeah, I overlooked that config.h is not the first to be included...