This function makes a better replacement for
gdk_display_get_core_pointer(), wherever it might yet be needed, for
XI2 resorts to XIGetClientPointer(), for the others return the only
core pointer.
https://bugzilla.gnome.org/show_bug.cgi?id=621685
Conceivably this GdkEventTranslator may still be asked for events such as
NoExpose or GraphicsExpose for pixmaps. It is not meant to translate such events,
but should at least behave with them.