'Process downloadable file paths.'

def process_doc(self, app, doctree):

    for node in doctree.traverse(addnodes.download_reference):
        targetname = node['reftarget']
        (rel_filename, filename) = app.env.relfn2path(targetname, app.env.docname)
        app.env.dependencies[app.env.docname].add(rel_filename)
        if (not os.access(filename, os.R_OK)):
            logger.warning(('download    file    not    readable:    %s' % filename), location=node, type='download', subtype='not_readable')
            continue
        node['filename'] = app.env.dlfiles.add_file(app.env.docname, filename)
