KT-6745: change message to reflect that a super qualifier should be an immediate supertype,

not just a supertype.

Author: dnpetrov

compiler/frontend/src/org/jetbrains/kotlin/diagnostics/rendering/DefaultErrorMessages.java

@@ -338,7 +338,7 @@ public String render(@NotNull BadNamedArgumentsTarget target) {
         MAP.put(SUPERCLASS_NOT_ACCESSIBLE_FROM_INTERFACE, "Superclass is not accessible from interface");
         MAP.put(AMBIGUOUS_SUPER, "Many supertypes available, please specify the one you mean in angle brackets, e.g. 'super<Foo>'");
         MAP.put(ABSTRACT_SUPER_CALL, "Abstract member cannot be accessed directly");
-        MAP.put(NOT_A_SUPERTYPE, "Not a supertype");
+        MAP.put(NOT_A_SUPERTYPE, "Not an immediate supertype");
         MAP.put(TYPE_ARGUMENTS_REDUNDANT_IN_SUPER_QUALIFIER, "Type arguments do not need to be specified in a 'super' qualifier");
         MAP.put(USELESS_CAST, "No cast needed");
         MAP.put(CAST_NEVER_SUCCEEDS, "This cast can never succeed");