fix library checks; implement client side of "touch" modify (ITS#4183)

tests/scripts/test004-modify

@@ -165,6 +165,10 @@ uidNumber: 1
 increment: gidNumber
 gidNumber: -1
 
+dn: dc=example,dc=com
+changetype: modify
+# EMPTY SEQUENCE OF CHANGE
+
 EOMODS
 
 RC=$?
@@ -174,6 +178,31 @@ if test $RC != 0 ; then
 	exit $RC
 fi
 
+echo "Using ldapmodify to add an empty entry (should fail with protocolError)..."
+$LDAPMODIFY -D "$MANAGERDN" -h $LOCALHOST -p $PORT1 -w $PASSWD \
+	 >> $TESTOUT 2>&1 << EOMODS
+dn: cn=Foo Bar,dc=example,dc=com
+changetype: add
+# EMPTY SEQUENCE OF ATTRS
+EOMODS
+
+RC=$?
+case $RC in
+2)
+	echo "	ldapmodify failed ($RC)"
+	;;
+0)
+	echo "	ldapmodify should have failed ($RC)!"
+	test $KILLSERVERS != no && kill -HUP $KILLPIDS
+	exit -1
+	;;
+*)
+	echo "	ldapmodify failed ($RC)!"
+	test $KILLSERVERS != no && kill -HUP $KILLPIDS
+	exit $RC
+	;;
+esac
+
 echo "Using ldapsearch to retrieve all the entries..."
 $LDAPSEARCH -S "" -b "$BASEDN" -h $LOCALHOST -p $PORT1 \
 	    'objectClass=*' > $SEARCHOUT 2>&1