Major changes in 2.22.4 are:
* Properly display submenus that are provided by extensions
* Preserve mtime when copying files
* Fix navigation where window was inconsistently "stuck" between two
  directories, i.e. the view was not completely changed.
* Icon view fixes
  * If no icon is selected, but an icon has the keyboard focus, select it when
    pressing space.
  * Move keyboard focus after a file has been removed
  * Fix double-clicking half-shown items
* Thumbnailing changes
  * Never scale up any thumbnails
  * Compose and scale thumbnails on the fly
  * Speed up loading of large image files used as their own thumbnails
  * Fix thumbnail regeneration