Use intra-xref for rootid

[cwickert]

We should use the intra-xref style for links that lead to the rootid of the current document. It may not be semantically correct, but it does makes sense because

1. there is no use linking to the very beginning, nobody wants to jump from within a document to its title.
2. it looks silly in some cases. A good example is the list of available documentation in doc-sle/xml/common_intro_available_doc_i.xml. All bullet points except the current document intra-xref, so one looks weirdly off and the link does not make sense.

So we not only need to check if the link target is outside the current rootid but if it is the rootid itself.

Hm, additionally, it might make sense to add "(this book)" after the title. However, that would need translation.

[janajaeger]

Does this still apply or can this be closed? Please have a look and decide how to proceed?