If GSS_C_INITIATE is specified, then get credentials from the
default cache. If we don't have any, then try using the keytab.
If GSS_C_ACCEPT is specified, just note our principal name and
open the keytab.
If GSS_C_BOTH is specified, do both of the above.
git-svn-id: svn://svn.h5l.se/heimdal/trunk/heimdal@10978 ec53bebd-3082-4978-b11e-865c3cabbd6b