Fixed broken scrolling of cached graphics items on X11.
Fixed broken scrolling of cached graphics items on X11.

The scrolling was broken in other graphics systems than the native,
since _q_scrollPixmap assumed that all QPixmaps were using the X11
backend. We can just use QPixmap::scroll instead, which should also make
it faster with the raster paint engine than creating a temporary painter
and doing a blit. Also, _q_scrollPixmap would do blending instead of
blitting for non-opaque pixmaps.

Reviewed-by: Olivier Goffart

pruiz/wkhtmltopdf-qt,radekp/qt,radekp/qt,radekp/qt,igor-sfdc/qt-wk,radekp/qt,pruiz/wkhtmltopdf-qt,pruiz/wkhtmltopdf-qt,pruiz/wkhtmltopdf-qt,igor-sfdc/qt-wk,radekp/qt,pruiz/wkhtmltopdf-qt,igor-sfdc/qt-wk,pruiz/wkhtmltopdf-qt,radekp/qt,igor-sfdc/qt-wk,pruiz/wkhtmltopdf-qt,radekp/qt,igor-sfdc/qt-wk,radekp/qt,igor-sfdc/qt-wk,pruiz/wkhtmltopdf-qt,igor-sfdc/qt-wk,radekp/qt,igor-sfdc/qt-wk,pruiz/wkhtmltopdf-qt,igor-sfdc/qt-wk,igor-sfdc/qt-wk,igor-sfdc/qt-wk,pruiz/wkhtmltopdf-qt,radekp/qt,pruiz/wkhtmltopdf-qt