Log Message:
gtk3+: updated to 3.24.21

Overview of Changes in GTK+ 3.24.21
===================================

* Wayland:
 - Prevent crashes with offscreen windows
 - Handle disorderly tablet/pad disconnects

* GtkFileChooser:
 - Translate the type column
 - Add a tracker3 search engine
 - Rate-limit trash monitoring
 - Make get_filter work for native chooser

* GtkGLArea:
 - Fix a redraw problem

* GtkScrolledWindow:
 - Fix kinetic scrolling

* Add a gtk-cursor-aspect-ratio setting

* GDK:
 - Improve frame clock smoothness
 - Fix frame clock monotonicity

* OS X:
 - Support Pen / Eraser input
 - Support openfiles in GtkApplication

* Adwaita:
 - Improve notebook tab legibility

* Translation updates:
 Basque
 Brazilian Portuguese
 Catalan
 Chinese (Taiwan)
 German
 Indonesian
 Italian
 Japanese
 Kazakh
 Lithuanian
 Polish
 Romanian
 Slovak
 Slovenian
 Swedish
 Ukrainian