Add an event_compression setting to GdkWindow

Setting event compression to false will allow inter-frame
mouse motion events to be delivered, which are necessary
for painting applications to produce smooth strokes.

https://bugzilla.gnome.org/show_bug.cgi?id=702392

gdk/gdkinternals.h

@@ -227,6 +227,7 @@ struct _GdkWindow
   guint applied_shape : 1;
   guint in_update : 1;
   guint geometry_dirty : 1;
+  guint event_compression : 1;
   GdkFullscreenMode fullscreen_mode;
 
   /* The GdkWindow that has the impl, ref:ed if another window.