Atom feed updates: Pagination

One of the hidden changes from last week's release is the support for Atom pagination.  This will potentially let tools browse of the entries in a blog, copy them, archive them, search them, etc.  Technically, this means we're supporting the link@rel="first", "last", "next", and "previous" relations.  Get the current feed and follow the "previous" links until you run out of data; then you've got all of the entries in a blog, in standard Atom format.  And, we're valid according to http://feedvalidator.org.  Let me know if you see any problems.