@param url: the URI of the actual mirror request
@type orig_resp: L{twisted.web2.http.Response}
@param orig_resp: the response from the cache to be sent to apt
- @rtype: L{twisted.internet.defer.Deferred}
- @return: a deferred that will be called back with the correct response
"""
log.msg('Checking if %s is still fresh' % url)
modtime = orig_resp.headers.getHeader('Last-Modified')