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.

/* preview style examples */
body {
	background-color:#EFEFEF;
	font:70% Verdana, Arial, Helvetica, sans-serif;
}