[NF] Improve replaceable base class error message.

Belonging to [master]:
  - #2944
  - OpenModelica/OpenModelica-testsuite#1126

Compiler/Util/Error.mo

@@ -472,7 +472,7 @@ public constant Message CIRCULAR_COMPONENTS = MESSAGE(170, TRANSLATION(), ERROR(
 public constant Message FAILURE_TO_DEDUCE_DIMS_FROM_MOD = MESSAGE(171, TRANSLATION(), WARNING(),
   Util.gettext("Failed to deduce dimensions of %s due to unknown dimensions of modifier %s."));
 public constant Message REPLACEABLE_BASE_CLASS = MESSAGE(172, TRANSLATION(), ERROR(),
-  Util.gettext("Class %s in extends %s is replaceable."));
+  Util.gettext("Class '%s' in 'extends %s' is replaceable, the base class name must be transitively non-replaceable."));
 public constant Message NON_REPLACEABLE_CLASS_EXTENDS = MESSAGE(173, TRANSLATION(), ERROR(),
   Util.gettext("Non-replaceable base class %s in class extends."));
 public constant Message ERROR_FROM_HERE = MESSAGE(174, TRANSLATION(), NOTIFICATION(),