Major changes in 3.21.92:
* Fix compiler warning (Dominique Leuenberger)
* Fix various places to work with Gtk+ 3.21.6
* Forbid dragging read-only events
* Updates translations for:
    * British English (David King)
    * Dutch (Hannie Dumoleyn)
    * French (Charles Monzat)
    * Gaelic (Fran Dieguez)
    * Korean (Seong-ho Cho)
    * Latvian (Rūdolfs Mazurs)
    * Lithuanian (Aurimas Černius)
    * Persian (Arash Mousavi)
    * Portuguese (Tiago Santos)
    * Scottish Gaelic (GunChleoc)
    * Swedish (Anders Jonsson)