CORBA24 — implementing import for C++

I'm concerned that for C++, implementing "import" as currently specified in
the Components spec will be extremely difficult.

Imagine how you might implement this: your IDL compiler generates a C++
header file for all imported name scopes and creates #include directives
for these files in the C++ code generated for the main IDL file. The main
problem is that importable name scopes are modules, interfaces, valuetypes,
structures, unions, and exceptions. To import an exception, for example,
the import mechanism would have to keep a dependency graph for that
exception type and make sure that all dependencies are generated into the
header file so the C++ compilation won't fail. This seems way too complex,
and I don't see the value of being able to import individual structs and such.

Remove structure, union and exception from the list of name scopes (and repository ids) that can be