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 url from future %}
{% load markup %}
{% load smiley_tags %}
{% load avatar_tags %}
{% avatar user "left" %}<a href="{% url 'bio-view_profile' username=user.username %}">{{ user.username }}</a>:<br />{{ msg|safe }}