Escape entities just before Pango rendering (#2382).

Escape entities just before Pango rendering (#2382).

Previously, text coming out of the player would have things like
& escaped to &.  This escaping is also done by libxml++ when
writing XML, so doing it in the player would mean it was done
twice.

We do, however, need to escape things before passing them to Pango
as otherwise it gives errors and renders nothing for the line.

Here we move the escaping to just before the rendering, meaning
that in the reset of DoM we should pass unescaped strings around.