Punt a set_cred_option() call down to the mechanism for the first
credential that we have whose mechanism implements a set_cred_option()
method.  Not completely sure this is the correct fix, as we may need to
change gssspi_set_cred_option() to keep going if it gets GSS_S_UNAVAILABLE
back from the mechanism-specific function (which is what the Kerberos
mechanism, previously the only provider of a set_cred_option(), returns
if it doesn't understand the request).

diff -up krb5/src/lib/gssapi/spnego/gssapiP_spnego.h krb5/src/lib/gssapi/spnego/gssapiP_spnego.h
--- krb5/src/lib/gssapi/spnego/gssapiP_spnego.h	2009-12-08 14:46:57.000000000 -0500
+++ krb5/src/lib/gssapi/spnego/gssapiP_spnego.h	2009-12-08 14:46:20.000000000 -0500
@@ -333,6 +333,15 @@ spnego_gss_inquire_sec_context_by_oid
 );
 
 OM_uint32
+spnego_gss_set_cred_option
+(
+	OM_uint32 *minor_status,
+	gss_cred_id_t cred_handle,
+	const gss_OID desired_object,
+	const gss_buffer_t value
+);
+
+OM_uint32
 spnego_gss_set_sec_context_option
 (
 	OM_uint32 *minor_status,
diff -up krb5/src/lib/gssapi/spnego/spnego_mech.c krb5/src/lib/gssapi/spnego/spnego_mech.c
--- krb5/src/lib/gssapi/spnego/spnego_mech.c	2009-12-08 14:47:01.000000000 -0500
+++ krb5/src/lib/gssapi/spnego/spnego_mech.c	2009-12-08 14:46:20.000000000 -0500
@@ -250,7 +250,7 @@ static struct gss_config spnego_mechanis
  	spnego_gss_inquire_sec_context_by_oid, /* gss_inquire_sec_context_by_oid */
  	NULL,				/* gss_inquire_cred_by_oid */
  	spnego_gss_set_sec_context_option, /* gss_set_sec_context_option */
- 	NULL,				/* gssspi_set_cred_option */
+ 	spnego_gss_set_cred_option,	/* gssspi_set_cred_option */
  	NULL,				/* gssspi_mech_invoke */
 	spnego_gss_wrap_aead,
 	spnego_gss_unwrap_aead,
@@ -2081,6 +2081,21 @@ spnego_gss_inquire_sec_context_by_oid(
 }
 
 OM_uint32
+spnego_gss_set_cred_option(
+		OM_uint32 *minor_status,
+		gss_cred_id_t cred_handle,
+		const gss_OID desired_object,
+		const gss_buffer_t value)
+{
+	OM_uint32 ret;
+	ret = gssspi_set_cred_option(minor_status,
+				     cred_handle,
+				     desired_object,
+				     value);
+	return (ret);
+}
+
+OM_uint32
 spnego_gss_set_sec_context_option(
 		OM_uint32 *minor_status,
 		gss_ctx_id_t *context_handle,