Qt: some work towards upgrading to version 5.5.1 (#971).

Addresses the issue about the Single Cell view: to simulate the N62
model with one or several graphs and with, for example, a 200,000 slow
down results in the plotting area repeatedly becoming black.

src/plugins/thirdParty/Qwt/src/qwt_plot_directpainter.cpp

@@ -253,9 +253,13 @@ void QwtPlotDirectPainter::drawSeries(
         if ( d_data->hasClipping )
             clipRegion &= d_data->clipRegion;
 
+/*---OPENCOR---
         canvas->installEventFilter( this );
+*/
         canvas->repaint(clipRegion);
+/*---OPENCOR---
         canvas->removeEventFilter( this );
+*/
 
         d_data->seriesItem = NULL;
     }