Fix https://bugzilla.gnome.org/show_bug.cgi?id=721517 #2
It conveys more clearly what this value means. https://bugzilla.gnome.org/show_bug.cgi?id=707649
To the XRandR and dummy backend (and as usual the dummy backend has no effect) https://bugzilla.gnome.org/show_bug.cgi?id=705670