mercurial/templates/paper/shortlogentry.tmpl

extensions: factor import error reporting out

To clarify third party extensions lookup, we are about to add a third place
where extensions are searched for. So we factor the error reporting logic out to
be able to easily reuse it in the next patch.

 <tr>
  <td class="age">{date|rfc822date}</td>
  <td class="author">{author|person}</td>
  <td class="description">
   <a href="{url|urlescape}rev/{node|short}{sessionvars%urlparameter}">{desc|strip|firstline|escape|nonempty}</a>
   {inbranch%changelogbranchname}{branches%changelogbranchhead}{tags%changelogtag}{bookmarks%changelogtag}
  </td>
 </tr>