Architecture support

Catching up after a bit of busyness on other fronts.  Everything looks good.

I did have a thought regarding repomd.xml that I thought would be good 
to bring up.  Sorry if this is a little late to bring up; it's not 
critical, but would be nice.

In apt, you can set up repositories such that the reference in 
sources.list is not architecture-specific.  This is possible because apt 
does some interpretation of the fields in sources.list and builds URIs 
from them using a standard algorithm.

Obviously, such a scheme can't be built into the rpm-metadata stuff. 
But we could allow for an architecture attribute on the metadata node, 
something like this:

<metadata arch="i386">
   <data type="primary"/>
   <data type="filelist"/>
   <data type="other"/>
   <data type="groups"/>
</metadata>
<metadata arch="powerpc">
   <data type="primary"/>
   <data type="filelist"/>
   <data type="other"/>
   <data type="groups"/>
</metadata>

The attribute could be optional, in which case it's assumed that the 
repository is correct.

What does everyone think of this?