patch 9.0.1178: a child class cannot override functions from a base class

Problem:    A child class cannot override functions from a base class.
Solution:   Allow overriding and implement "super".
diff --git a/src/errors.h b/src/errors.h
index d12eb9f..6fa1abb 100644
--- a/src/errors.h
+++ b/src/errors.h
@@ -3432,4 +3432,10 @@
 	INIT(= N_("E1353: Class name not found: %s"));
 EXTERN char e_cannot_extend_str[]
 	INIT(= N_("E1354: Cannot extend %s"));
+EXTERN char e_duplicate_function_str[]
+	INIT(= N_("E1355: Duplicate function: %s"));
+EXTERN char e_super_must_be_followed_by_dot[]
+	INIT(= N_("E1356: \"super\" must be followed by a dot"));
+EXTERN char e_using_super_not_in_class_function[]
+	INIT(= N_("E1357: Using \"super\" not in a class function"));
 #endif