When compiled with GTK3 if an image is opened with "View in new window"
the minimum window size is determined by the image size and screen size
etc. If a file selection is opened, the minimum window size is set by
the first image displayed.
This feature is determined by a call to gtk_widget_set_size_request().
When compiled with GTK2, the call to gtk_widget_set_size_request() seems
to be ignored, and the window can be resized at will.
The GTK2 style is much more practical, so the call to
gtk_widget_set_size_request() is ignored in GTK3.
req_size.height = h;
gtk_widget_size_allocate(GTK_WIDGET(vw->window), &req_size);
+#if !GTK_CHECK_VERSION(3,0,0)
gtk_widget_set_size_request(vw->imd->pr, w, h);
+#endif
gtk_widget_show(vw->window);