[rfc-i] references vs front matter

[Julian Reschke]

Paul Hoffman wrote:
>> For xml2rfc that could give you an unused reference error.
> 
> Just for the record: that is irrelevant to the question of what the 
> RFC should look like. xml2rfc is a tool that is used to produce RFCs. 
> If the tool isn't producing them correctly, then we should fix the 
> tool.

rfc2629.xslt already reminds the author that if an RFC is being 
obsoleted or updated, it should be mentioned somewhere in the text as 
well (yes, that's my preference).

BR, Julian