CORBA24 — Minor glitch about forward declared things

When value types added forward declarations, and when we added forward
declarations for structs and unions, we forgot to update the version pragma
text. Currently, it says (page 10-45):

Attempts to assign a prefix to a forward-declared interface
and a different prefix to that interface later result in
a compile-time diagnostic:

Proposal:

Change that sentence to read:

Forward-declared constructs (interfaces, value types, structures,
and unions) must have the same prefix in effect wherever they appear.
Attempts to assign conflicting prefixes to a forward-declared
construct result in a compile-time diagnostic. For example:

Add the following clarification: