ITCR — Errors on code snippet related to skeleton classes

There is an error in 6.25.6 related to the skeleton classes. The skeleton classes should derive from each other, not from the traits, so it should be as below, also C_skel is lacking.

// C++
class A_skel : public virtual PortableServer::ServantBase {};
class B_skel : public virtual A_skel {};
class C_skel : public virtual A_skel {};
class D_skel : public virtual B_skel, public virtual C_skel {};

The other code bits in this section also have to be checked and see if they are ok.

Correct skeleton inheritance

The traits shouldn't be used in this example, those are for user code.