[Rpm-metadata] xml update

[seth vidal]

> I think we'd want to either nail down a standard priority regime or set
> up translation tables first.
> 
> Maybe priority regimes could be set as an attribute?
> 
> <priority system="debian">required</priority>
> 

But where does this data come from?

I don't have a problem about this being in the common area - but It has
to be optional - b/c if all I have a is a dir of rpms then this data
isn't present.

-sv