As Windows SSPI authentication calls fail when a particular mechanism
isn't available, introduced these functions for DIGEST, NTLM, Kerberos 5
and Negotiate to allow both HTTP and SASL authentication the opportunity
to query support for a supported mechanism before selecting it.
For now each function returns TRUE to maintain compatability with the
existing code when called.
This is a follow up to the parent commit dcdd4be which fixes one leak
but creates another by failing to free the credentials handle if out of
memory. Also there's a second location a few lines down where we fail to
do same. This commit fixes both of those issues.
