QPicture: don't hold images in QList

QImage is larger than a void*, so holding them in a QList is needlessly
inefficient. Worse, the code could come to depend on the fragile property
of (inefficient) QLists that references to elements therein never are
invalidated.

Change-Id: I153995d691692f7317cab31b95a00d679f31c0af
Reviewed-by: Konstantin Ritt <ritt.ks@gmail.com>
Reviewed-by: Gunnar Sletta <gunnar@sletta.org>

src/gui/image/qpicture_p.h

@@ -151,7 +151,7 @@ public:
     QRect override_rect;
     QScopedPointer<QPaintEngine> paintEngine;
     bool in_memory_only;
-    QList<QImage> image_list;
+    QVector<QImage> image_list;
     QVector<QPixmap> pixmap_list;
     QList<QBrush> brush_list;
     QList<QPen> pen_list;