Unify auth schemes credential states.

Unify auth schemes credential states.

Each scheme was maintaining it's own fields about what the state of the
credentials was.
This allows code to determine the state of the credentials easily.
Username cache can also display the credential state of any auth type now.

Tested on Basic, not yet tested for Digest, NTLM, Negotiate.

Also: fixed error where Negotiate always reported no program configured.