gss: SAnon - the Simple Anonymous GSS-API mechanism

Add support for SAnon, a simple key agreement protocol that provides no
authentication of initiator or acceptor using x25519 ECDH key exchange.
See doc/standardization/draft-howard-gss-sanon-xx.txt for a protocol
description.

tests/gss/check-basic.in

@@ -125,22 +125,25 @@ ${acquire_cred} \
 
 echo "keytab w/ wrong name"
 ${acquire_cred} \
-    --acquire-type=accept \
+    --acquire-type=accept --kerberos \
     --acquire-name=host@host2.test.h5l.se 2>/dev/null && exit 1
 
 echo "init using keytab"
 ${acquire_cred} \
+    --kerberos \
     --acquire-type=initiate \
     --acquire-name=host@host.test.h5l.se > /dev/null || exit 1
 
 echo "init using keytab (loop 10)"
 ${acquire_cred} \
+    --kerberos \
     --acquire-type=initiate \
     --loops=10 \
     --acquire-name=host@host.test.h5l.se > /dev/null || exit 1
 
 echo "init using keytab (loop 10, target)"
 ${acquire_cred} \
+    --kerberos \
     --acquire-type=initiate \
     --loops=10 \
     --target=host@host.test.h5l.se \
@@ -163,6 +166,7 @@ ${acquire_cred} \
 
 echo "init using existing cc"
 ${acquire_cred} \
+    --kerberos \
     --name-type=user-name \
     --acquire-type=initiate \
     --acquire-name=user || exit 1
@@ -171,12 +175,14 @@ KRB5CCNAME=${nocache}
 
 echo "fail init using existing cc"
 ${acquire_cred} \
+    --kerberos \
     --name-type=user-name \
     --acquire-type=initiate \
     --acquire-name=user 2>/dev/null && exit 1
 
 echo "use gss_krb5_ccache_name for user"
 ${acquire_cred} \
+    --kerberos \
     --name-type=user-name \
     --ccache=${cache} \
     --acquire-type=initiate \
@@ -194,11 +200,13 @@ KRB5_KTNAME="${keytab}"
 
 echo "init using keytab"
 ${acquire_cred} \
+    --kerberos \
     --acquire-type=initiate \
     --acquire-name=host@host.test.h5l.se 2>/dev/null || exit 1
 
 echo "init using keytab (ccache)"
 ${acquire_cred} \
+    --kerberos \
     --acquire-type=initiate \
     --ccache=${cache} \
     --acquire-name=host@host.test.h5l.se 2>/dev/null || exit 1