This is the new recommended approach since gdk_input_{add,remove} were
deprecated (and, honestly, seems a lot more sensible - why on earth
would those functions have lived in *GDK* of all places?). The old
implementation is preserved under ifdef for GTK1.
This was the last of the GDK deprecated functions to go! So GTK PuTTY
now compiles cleanly with -DGDK_DISABLE_DEPRECATED in addition to all
the other precautionary flags (though if you do that, you disable GDK
rendering, which greatly slows down server-side font handling). This
completes the GTK2-compatible preparation phase of the GTK 3 migration
guide.