[Oberon] Clarifying type compatibility in Oberon-07

[Jörg]

    > So I agree with Артур Ефимов, probably Wirth will update the language report soon.
    
    I really hope that won't happen. If one wants structural equivalence
    then there is Modula-3.
    
Hopefully, he will not do it. As explained I see no good reason to do so.
Jörg