When accepting, do not leak a name if the underlying mech reports a
src_name twice. Record mech_type and delegated_cred_handle and report
them to the caller at the final SPNEGO step, not when the underlying
mech reports them.
When initiating or accepting, report ret_flags at every step, and
filter out PROT_READY as required by RFC 4178 section 3.1. Report a
time_rec value at the final step even if we didn't call into the
underlying mech, using a call to gss_context_time() if necessary.
In the mechglue, initialize ret_flags and time_rec for both
gss_initialize_sec_context() and gss_accept_sec_context().