Restore persistent userpaint functionality in slideshow.

This was part of i103174 - Code from the ecntablet and eraser CWS;
optionally improves user paint interactions in slideshow, and got
accidentally cleaned away for being commented out.

Change-Id: I4fb87a3e1cb834e10ae766ed8c58cd6f2397c45f
diff --git a/sd/source/ui/slideshow/slideshowimpl.cxx b/sd/source/ui/slideshow/slideshowimpl.cxx
index afc85dc..3350675 100644
--- a/sd/source/ui/slideshow/slideshowimpl.cxx
+++ b/sd/source/ui/slideshow/slideshowimpl.cxx
@@ -1422,6 +1422,13 @@ void SlideshowImpl::displayCurrentSlide (const bool bSkipAllMainSequenceEffects)

void SlideshowImpl::endPresentation()
{
    if( maPresSettings.mbMouseAsPen)
    {
        Reference< XMultiServiceFactory > xDocFactory(mpDoc->getUnoModel(), UNO_QUERY );
        if( xDocFactory.is() )
            mxShow->registerUserPaintPolygons(xDocFactory);
    }

    if( !mnEndShowEvent )
        mnEndShowEvent = Application::PostUserEvent( LINK(this, SlideshowImpl, endPresentationHdl) );
}