I made these changes on moodle.org ...

• • • 2873,2888 ****
      // Print shortened version
      echo format_text(forum_shorten_post($post->message), $post->format, $options, $course->id);
      $numwords = count_words(strip_tags($post->message));
      ! echo '<p><a href="'.$CFG->wwwroot.'/mod/forum/discuss.php?d='.$post->discussion.'">';
      echo get_string('readtherest', 'forum');
      ! echo '</a> ('.get_string('numwords', '', $numwords).')...</p>';
      } else
      Unknown macro: { // Print whole message if ($highlight) { echo highlight($highlight, format_text($post->message, $post->format, $options, $course->id)); } else { echo format_text($post->message, $post->format, $options, $course->id); }
      echo $attachedimages;
      }
      
      — 2876,2893 ----
      // Print shortened version
      echo format_text(forum_shorten_post($post->message), $post->format, $options, $course->id);
      $numwords = count_words(strip_tags($post->message));
      ! echo '<div class="posting"><a href="'.$CFG->wwwroot.'/mod/forum/discuss.php?d='.$post->discussion.'">';
      echo get_string('readtherest', 'forum');
      ! echo '</a> ('.get_string('numwords', '', $numwords).')...</div>';
      } else {
      // Print whole message
      + echo '<div class="posting">';
      if ($highlight) { echo highlight($highlight, format_text($post->message, $post->format, $options, $course->id)); } }
      else { echo format_text($post->message, $post->format, $options, $course->id); }
      + echo '</div>';
      echo $attachedimages;
      }

Please let me know if that's exactly what you needed and if it is then I'll check it into 1.9 and HEAD as well.