Comment 1 for bug 897537

The URL is, for example, <http://bazaar.launchpad.net/+branch/python-fixtures/tarball/42> or <http://bazaar.launchpad.net/+branch/python-fixtures/tarball> so the webapp can fairly easily just synthesize this, given the branch and the revision (if any) it wants.

The open questions are:
 * which pages should this be on
 * where should it be on the page
 * what should it be called
 * what should it look like