mod_pubsub_serverinfo: Warm-up opt-in cache By warming up the cache that contains the opt-in data, the first publication has a better chance of including domain names for remote domains that opt-in. Without this change, those domains are named only after the _second_ publication, which can take a while. New users are likely thrown off by that.

<tr>
  <th>What is {x} {op} {y}?</th><td>
    <input name="captcha_challenge" type="hidden" value="{challenge}">
    <input name="captcha_reply" pattern="[0-9]+" required type="number">
  </td></tr>