Fixing #230; add a scrollbar to the PM popup dialog if necessary. This wasn't as easy as I thought. Had to wrap the PM text in a div with its styling (max-height and overflow). If I then resized the dialog, I'd get two scrollbars. So for now, made the dialog non-resizable.

{% load core_tags %}
<p>
<span class="shoutbox-user">{{ shout.user.username }}:</span>
<span class="shoutbox-shout">{{ shout.html|safe }}</span><br />
<span class="shoutbox-date">{{ shout.shout_date|elapsed }}</span>
</p>